Java Databases Stuff

DEPARTMENT OF COMPUTER SCIENCE

CO7101 Java & Databases For Bioinformatics

Course Notes 2014

Dr. S. Kerrigan

Foreword These notes are to accompany the module CO7101. They contain material that goes beyond the core knowledge of this course. For more motivation and background please attend the lectures. These notes are detailed. Thus, while they should be useful and have been checked carefully, there may be some errors. Please do let me know about any typos or other mistakes which you find. If you have any other (constructive) comments, please tell me about them. If you are to do well in this course, YOU MUST ATTEND THE LECTURES. They will give you additional examples, highlight key issues which may not appear quite as important from the notes as in fact the issues are, and give guidance towards what you need to know for the examinations. You should note especially that with a course of this nature, notation, definitions and ideas can differ even among the experts. The lectures will clarify many of the more woolly areas. It is recommended you purchase the following books to accompany these notes:-

1. An Introduction to Object-Oriented Programming with Java, 5th Edition by C. Thomas Wu (Otani), Naval Postgraduate School

2. Database Systems: A Practical Approach to Design, Implementation and

Management, 5th Edition, Thomas M. Connolly, Carolyn E. Begg

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CO7101: Java & Databases For Bioinformatics

Relational Databases 1:

CO7101: Java & Databases For Bionformatics

1


Dr. Stuart Kerrigan

Material in this Unit by Dr. Nick Measor, Dr. Stephan Reiff-Marganiec and Dr. Naila Rhaman

Before Databases: File‐Based Approach to Information Systems (up to 1980s)

A collection of application programs that perform

services for the end‐users such as answering queries and production of reports.

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and production of reports.

Each program defines and manages its own data,

so we may have data redundancy, inconsistency

and duplication.

Library Example

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Library needs to manage:

the book cataloguebook loansbook reservationsrecall of overdue loanscatalogue inquiriesmembership. . .

Traditional file approach

• Library‐user file:– information about each library user.

• Catalogue file:– information about books in the library.

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• Loans file:– information about each book on loan and the person

who is borrowing the book.

• Reservations file:– information about each book reserved and the person

who is reserving the book.

The filesLibraryusers

Catalogue

5

Loans

Reservations

Example of file: The library users

D. Andrews 14 High Street Oadby Leicester LE2 5HE tel: 274 4893 loan-status: Adult

57-AD-97

d

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Library- users

D. Andrews 14 High Street Oadby Leicester LE2 5HE tel: 274 4893 loan-status: Adult

57-AD-97

2

Traditional file‐based approach

ReservationInformation

LoanInformation

OverdueLetters

CatalogueInquiry

LoanProcess

ReservationProcess

OverdueLoans Process

CatalogueInquiryProcess

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ProcessProcess Loans Processq yProcess

Reservationsfile

Cataloguefile

Library-usersfile

Loansfile

NOTE: The processes must relate data between the files when necessary

Another approach – a single file

Why not put all the information in a single table –such as an Excel spreadsheet?

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Name Address Telephone Status Book title

Book author

ISBN Date borrowed

And so on with further cells supplying all the inform

Duplication of information in the single file approach

Name Address Telephone Status Book title Book author

ISBN Date borrowed

D. 14 High 274 4893 Adult Donatello Green 123- 12/04/

9

Andrews Street halgh 4567 2006

D. Andrews

14 High Street

274 4893 Adult War and Peace

Tolstoy 456-1234

18/05/2006

Summary of file‐based system disadvantages

• Separation of data

• Duplication of data: wasteful, loss of data integrity.

• Data dependence ‐ difficult to change the structure of data, unresponsive to updates, extensions, d l hi h d l

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redevelopment: high development cost

• Incompatible file formats

• Fixed queries, difficult to do ad hoc queries

• Low reliability, security, integrity

The solution – use a database

Important points to remember:

A shared collection of logically related data

(and a description of this data) designed to

meet the information needs of an organisation.

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• shared• collection• self‐describing• logically related:

– entities– attributes– relationships

Definition of DBMS

a DBMS provides the following facilities:

A software system that enables users to define, create and maintain the database and provides

a controlled access to this database.

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• Data Definition Language: data types and structures

• Data Manipulation Language: query language (e.g. SQL)

• Controlled access to the database– a security system

– a concurrency control system

– an integrity system

– a recovery control system

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Database Advantages

• consistent and structured model of data

• efficient electronic filing cabinet: no need to control data

d h i

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• ad hoc queries

• easy to update, change structure

• concurrency: sharing data

• improved security

The main idea

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Model the world

User’s model of a library

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System rules

1. A copy of a book can only be lent to one person at a time.

2. A person may borrow several books at a time.

3. Each person has a status in the library which determines such things as loan period, max. books on loan, overdue fees.

Modelling the world

applications information available

h

modelMy model

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database

databasedesign

datamodel

information desired

the same?

Start

Entity‐Relationship Model of the Library

CopyOf

Author

nameauthor-details

Writtenby

Catalogue

isbn

date 0..*0..*title

publisher

1

res-date

0..*

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Book

copy#accession-date

CopyOf

0..*

Reserves0..*

Library-user

user#nameaddresstel

loan-date

IsonLoan

0..10..*

Status

idstatus-details

HasStatus

0..* 1

Implementer’s model of the

library

Book(copy#, isbn, accession_date)primary key: copy#foreign key: isbn references Catalogue(isbn)

Library-user(user#, name, address, tel, status)primary key: user#foreign key: status references Status(id)

Loan(copy#, user#, date)primary key: copy#, user#foreign key: copy# references Book(copy#)foreign key: user# references Library-user(user#)

The relation schemas:

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Catalogue(isbn, title, publisher, date)primary key: isbn

Reservation(user#, isbn, date )primary key: user#, isbnforeign key: user# references Library-user(user#)foreign key: isbn references Catalogue(isbn)

Written-by(isbn, name)primary key: isbn, nameforeign key: isbn references Catalogue(isbn)foreign key: name references Author(name)

Status(id, details )primary key: id

Author(name, details)primary key: name

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The Story of Larry The Lion

Dr. Stuart Kerrigan

Objectives

• The terminology of the relational model

– Candidate, primary and foreign keys

• How to use relations to model

i i– entities

– relationships between entities

• Integrity rules for relational model

• Queries

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Definition of Data Model

There are three components of each data model:• a structural part — rules for constructing databases terminology

An integrated collection of concepts for describing data, relationships between data, and constraints on the data.

a structural part rules for constructing databases, terminology• a set of integrity rules to ensure data accuracy• a manipulative part — defines the type of operations that

are allowed on the database

There are object‐based, relational, and other data models. Here we consider the relational model.

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Past and Present of RM

• The relational model was originally described by E.F. Codd in his 1970 paper

– “A relational model of data for large shared data banks’’

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History

• Three projects that started it all in late 1970s– System R, by IBM in late 1970s

• Structured Query Language (SQL) developed

• commercial products: SQL/DS and ORACLE

– INGRES, Uni. of California at BerkeleyG S, U o a o a at e e ey• relational DBMS Ingres

– Peterlee Relational Test Vehicle, IBM UK• query processing, optimization, functional extensions

• Commercially available PC versions of RDBMSs– Access and FoxPro from Microsoft

– Paradox and Visual dBase from Borland

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Entities

An entity is a

– thing

– object

concept– concept

in the real world

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Can be distinguished from other objects.

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Attributes

• An attribute is a property of an entity

• An object can be described by a set of properties:

O i l id tif bj t (k )– One may uniquely identify an object (key)

– Others may add (useful) information

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Modelling Entities in the Real World

“entity”

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representedby a name and

a set ofattributes

Terminology

• A set of entities of the same type is represented as a table (also called relation)

• Each row in the table represents an entity

h l ib• Each column represents an attribute

• An atomic place in a table is called a cell

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Different Terminology

User Relational Model

Programmer

Table Relation Fileor

Array

Row Tuple Record

Column Attribute Field

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A Relation About Film Stars

Starname yob sex country

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Marlon Brando 1924 Male USAHarrison Ford 1942 Male USADustin Hoffman 1937 Male USARobert Redford 1937 Male USAMeryl Streep 1949 Female USA

Properties of Relations

• Relations have names

• Each cell of the relation contains one atomic value

• Each attribute (column) has a distinct name

• Values of attributes come from the same domain

• The order of attributes is irrelevant• The order of attributes is irrelevant

• The number of columns (attributes) is called degree

• Each tuple (row) is distinct

• The order of tuples is not significant, theoretically

• The number of rows (tuples) is called cardinality

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6

Keys

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uniquely identifies entity

a1 a3 a4a2

Identify?

What is meant by identify?

Real World a set of values will take you to a unique object (entity)

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unique object (entity).

Model a set of values will take you to a unique row (tuple).

Really the same: an object in the real world is modelled by a row in a table.

Keys

identifies a unique row in a table Larry

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key

identifies anobject in the world row is modelling

the object

Larry Lion

Superkeys

• A superkey is a set of one or more attributes that uniquely identifies an entity within a relation

• Superkeys always exist — just take all p y y jattributes

• For example, – name, weight and age in Animal

– family and food in Diet

– type in Food

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Candidate Keys

Let R be a relation schema (relation name followed by a list of attribute names). A subset I of the attribute names of R is called a candidate key if:candidate key if:

– No two distinct tuples of the relation can take the same values on I (Uniqueness) (in other words, I is a superkey)

– No proper subset of I satisfies the above rule (Irreducibility)

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Primary Keys

• The primary key is the candidate key that is selected to identify tuples uniquely within the relation

• Relationships between different keys:Relationships between different keys:

– There can be many superkeys. Some of the superkeys are candidate keys. One of the candidate keys is the primary key.

– A candidate key is a superkey such that no proper subset of it is a superkey within the relation

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Example

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registration make model colour

Car(registration, make, model, colour)

Underline: primary key

The zoo has another problem

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The zoo obtained a new animal — Larry the Leopard

Primary Key

• Name used as primary key

• But we cannot have two animals with the same primary key!

ibl l iwhich Larry?

• Possible solutions:

– change Larry's name

– key becomes name + family

– introduce a new artificial key

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similar problems, what happens if another leopard

called Larry arrives?

y

surrogate key

Relationships

• An association between two or more entities

• Identified/described by two or more key attributes

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Star Filmrole

cast_asEntity Type Entity Type

Relationship

Relationships Represented by Tables

Given the Film Star table and the Film table, an example of a relationship between these tables is the Role relation (table):

RoleRole

Name Film Cast_As

Harrison Ford Star Wars Han Solo

Harrison Ford Raiders of the Lost Ark

Indiana Jones

Marlon Brando

Last Tango In Paris Paul

Tables

• A table models:

– objects in the real world

– relationships between objects (entities)

I ll t bl i ll d “ l ti ”• In all cases a table is called a “relation”

42

8

Relation Schema Definition

Relation schema is a set of attribute names and theirdomains.

DomainsAttribute names

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CHARACTER(25)CHARACTER(10)

SMALLINT

namenationalityyob

Player(name, nationality, yob)

Example of Relation

(Tom Watson , USA, 1949)(Jack Nicklaus, USA, 1940)

A set of tuples for relation Player

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( , , )(Severiano Ballesteros, Spain, 1957)(Raymond Floyd, USA, 1942)

Values ofattribute

name

Taken fromdomain

CHARACTER(25)

A Better Definition of Relation

• Given a relation schema, a relation or tabledefined for that schema is a finite set of tuples such that:

– Each tuple contains as many values as there are– Each tuple contains as many values as there are attribute names in the relation schema.

– Each value is drawn from the domain with which its attribute (column) type is associated.

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Foreign Keys

• Recall:

– There may be more than one candidate key

– We may choose a particular one and called it the primary key

• A foreign key is an attribute (or a set of attributes) that matches the candidate key of some relation

• Examples: keeper attribute in the Animal table, or supervisor in the Managed‐by table

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Examples

name family weight age keeper

Larry lion 500 4 112Ernie elephant 4000 3 724Sydney snake 1000 6 134. . .

Animalforeign key

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Keeperpersonnel_no name age

112 Jones 34724 Thomas 42134 Brown 25. . .

Relational Integrity

• Relational integrity is a set of rules which ensure that the data is accurate

• The rules contain:– Domain constraints (we have already met theseDomain constraints (we have already met these constraints)

– Entity integrity rule

– Referential integrity rule

• Before we define the last two rules, we study the concept of nulls

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Nulls

• Null represents a value for an attribute that is currently unknown or it is not applicable.

• Null is not the same as

– numeric value zero

– string of spaces

• Not all RDBMS use nulls. If we don’t use nulls, then we need to use “false’’ data to represent missing or non‐applicable data. For example, use number ‐1 in the field of type text.

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Entity Integrity

• Recall: Entities are modelled by tables. Each table has a primary key.

• Entity Integrity:

In a table no cell under a primary

• For example, in the Animal table no record can have a null in the name column; and in the Food table there may be no nulls in the type (of Food) column

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In a table, no cell under a primarykey column can be null.

Referential Integrity

If a foreign key exist in a table, either the foreignkey value must match a candidate key value ofsome row in its home table, or the foreign key valuemust be null.

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For example, we cannot have a record in the Animal table with 700 in the keeper cell, unless there is a keeper 700 in the Keeper table. But, we can have an animal with null value under keeper: the new arrival (Larry the Leopard) has not yet been assigned to a particular keeper.

Queries

• How to search for specific data in the database?– Example: list all animals eating buns with weight between 20 and 200 kg, in ascending order of their age

• DBMS supports flexible queries of the data• QBE (Query‐by‐example): a visual way of specifying a Q (Q y y p ) y p y gquery

• SQL (Structured Query Language): a language for specifying queries to a relational database– de facto standard– Use English words, e.g. SELECT, INSERT, WHERE…

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QBE and SQL

• QBE can be regarded as a graphical “front‐end” to SQL

• They are non‐procedural languages: you specify whatyou want, not how to get it

• Some operations:Some operations:– Update data– Search data according to some criteria– Display results in certain order– Aggregate functions (max, sum, …)

• In the practicals, you will learn how to use QBE in Access

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Summary

• A relational database consists of nothing but relations represented as tables

• A table can represent either an entity set or a relationship between entities

• Each table has a predefined and time‐invariant format — this is specified by the relation schema

• Each table is homogeneous — each column contains only values from a specified domain

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Summary: Terminology

• Entity a real‐world object / concept• Entity set a collection of entities• Attribute a property of an entity• Relation a “table” with columns and rowsT l i t bl• Tuple a row in a table

• Relationship an association between two or more entities

• Database a set of tables for entity sets and relationships

• Rel. Database a collection of normalized tables

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CO7101 Java & Databases

Entity Relationship Diagrams

CO7101 Java & Databases 56

Entity Relationship Diagrams

Dr. Stuart Kerrigan

Objectives

• The use of conceptual models to support database design

• Basic concepts of Entity‐Relationship (ER) model: entities attributes relationshipsmodel: entities, attributes, relationships

• Types of relationships

• Diagrammatic technique for displaying ER models

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The Database Design Process

• Step 1: Construct a conceptual model (typically ER model) to capture precisely the real‐world problem

• Step 2: Design database tables to represent• Step 2: Design database tables to represent the ER model

• Step 3: Implement the tables in a DBMS

• We will now start Step 1…

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Conceptual Modelling

• The process of constructing a model for certain information that is independent of implementation issues such as

– The type of DBMS

– Application programs

– Programming language

– Other physical considerations

• The conceptual model should be a complete and accurate representation of the required information

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The Entity‐Relationship (ER) Model

• The ER model is a high‐level conceptual model proposed by P.P. Chen in 1976 in the paper

– “The Entity‐Relationship model ‐ towards a unified view of data’’

• Purpose of ER model:

– Support user’s understanding of information

– Abstract from technical details of database design

– Be independent of DBMS and hardware issues

60

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Entity‐Relationship Modelling

• Entity‐Relationship modelling: identify what information we want to describe, and structure that information in a sensible way

• How do we do this?• How do we do this?

– identify entities

– identify attributes

– identify relationships

between entities

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The basic concepts of ER modelling

Entities

• An entity is something that makes sense in an application context:

– a tangible and/or visible thing

something that may be apprehended intellectually– something that may be apprehended intellectually

– something toward which thought or action is directed

– something about which information needs to be recorded

62

Entities and Their Representation

63

Car(reg#,make,model) XTX456A Nissan Bluebird

instance of a carconcept of a car

Entities vs. Entity Types

• Entity type: an object or a concept that is identified by users as having an independent existence– Examples: car, employee, sale

• Entity: an instance of an entity type that is uniquely identifiable– Examples:

• John Smith, L1328, 1 High Street, ...

• XTX456A Nissan Bluebird, 1023, £1234,...

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Attributes

• An attribute is an abstraction of a single characteristic or property of an entity or a relationship type

• Entities are identified by their properties, i.e. by sets of values held by attributes

• Attribute domain is a set of values that may be assigned to an attribute

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Attribute Values for a Car

66

Attributesregistration#makemodel

MVI 321BMW316

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Finding and Classifying Attributes

• Naming attributes: used to uniquely identify an entity– Usually don’t change

– “What uniquely identify this object from other q y y jsimilar objects (same entity set)?”

• Descriptive attributes: provide intrinsic information about the entity– “what properties distinguish this entity (from other entity types)?”

67

Simple vs. Composite Attributes

• Simple attribute: composed of a single component, with an independent existence

• Composite attribute: composed of multiple components each with an independentcomponents, each with an independent existence

– For example, Address: contains number, street, town, ... components.

68

Single‐ vs. Multi‐valued Attributes

• Attributes are either single‐ or multi‐valued depending on the number of values they hold

– Examples:

• Tel_No: one may have more than one telephone number

• Gender: one can only have one gender

• Type_of_food: a dish may consist of several types of food: protein, carbohydrates,...

• What is the difference between composite and multi‐valued attributes?

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Derived Attributes

• Derived Attribute: an attribute whose value is derivable from the values of other attributes, not necessarily in the same entity

– Examples:– Examples:

• Age is derivable from DoB

• Total_Staff (of, say, the Department entity) can be calculated by counting Staff entities

70

ER Diagrams: Entities and Attributes

Employee

NI#[PK]name

fi t

Entity name

Primary key

Composite

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firstnamelastname

dob/ageskills[1..3]

Attributes

Derivedattribute

Multi-valuedattribute

Compositeattribute

Relationships

XBS 456 NFordZodiac P#351

John Smith1 Hi h St t

There are relationships between entities: My car

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1 High StreetLeicester

P#351 owns XBS 456 N

Relationship: an association of entities, where the association includes one entity from each participating entity type

13

Representing Relationships

73

Owner

personnel-no[PK]namestreettown

ownsCar

reg#[PK]makemodel

Relationship: Notation

Entity_type_name_2

attribute_3attribute_4

Entity_type_name_1

attribute-1attribute-2

relationship

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Staff Next_of_KinRelatedTo

Example:

Relationship: Some Terms

• Degree of a relationship: the number of participating entities in a relationship– binary

– ternary

quaternary– quaternary

– unary (recursive)• Example: “Supervises” between the entities Keeper and Keeper

• Relationships may be given role names to indicate the purpose that each participant plays in a relationship

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Structural Constraints on Relationships

• There are cardinality and participation constraints

• Cardinality ratio (or multiplicity): describes the number of possible relationships for each participating entityparticipating entity

• For binary relationships, cardinality ratios are– one‐to‐one– one‐to‐many– many‐to‐one– many‐to‐many

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Kinds of Relationship – 1

• One‐to‐One

– Every warehouse has no more than one manager

– Every member of Staff can manage at most one warehousewarehouse

77

0..1

Warehouse

0..1

Staff

0..10..1

Manages

One‐to‐One Relationships

a1

a b

78

a2

a3 b2

b3

b1

14


• Many‐to‐One

– Every employee works at no more than one warehouse

– Every warehouse has several (>=0) employeesEvery warehouse has several (>=0) employees working in it

79

0..1

Warehouse

0..*

Employee

0..10..*

Works_in

Many‐to‐One Relationships

a1

a2b1

80

a5

a3

a4

b2

b3


• One‐to‐Many

– Each manager supervises several employees

– Every employee is supervised by only one managermanager

81

0..*

Employee

0..1

Manager

0..*0..1

Manages

One‐to‐Many Relationships

a1

b1

b2

82

a2

a3

b5

b3

b4


• Many‐to‐Many

– Each student takes several (>=0) modules

– Each module is taken by a number (>=0) of studentsstudents

83

0..*

Course

0..*

Student

0..*0..*

Takes

Many‐to‐Many Relationships

a1 b1

84

a2

a3

a4

b2

b3

b4

15

Some Examples

• What is the cardinality ratio of these relationships?

– Entity sets: Males, Females

– Relationship: is‐married‐to

– Entity: Animals, Families

– Relationship: belongs‐to

– Entity: Books, Users

– Relationship: is‐reserved‐by

85

Participation Constraints

• Determine whether the existence of an entity depends upon it being related to another entity through the relationship.

• If an entity’s existence requires the existence of an associated entity in a particular relationship, then participation is total. Otherwise, it is partial.

• Total and partial participation are often referred to as mandatory and optional, respectively.

86

Membership Class – 1

• Mandatory (total) both sides:

– A student must attend at least one lecture

– A lecture must be attended by at least one studentstudent

87

Student membership is mandatory.Lecture membership is mandatory.

1..*

Lecture

1..*

Student

1..*1..*

Attends


• Mandatory one side and optional the other side:

– A student must attend at least one lecture

A lecture need not be attended by any students– A lecture need not be attended by any students

88

Student membership is mandatory.Lecture membership is optional.

1..*

Lecture

0..*

Student

1..*0..*

Attends


• Optional both sides:

– A student need not attend any lectures

– A lecture need not be attended by any students

89

Student membership is optional.Lecture membership is optional.

0..*

Lecture

0..*

Student

0..*0..*

Attends

Strong vs. Weak Entity Types

• Strong entity type: an entity type that is not dependent on the existence of another entity type for its primary key– For example, Staff, Library_User, ...

Has its own primary key– Has its own primary key

• Weak entity type: an entity type that is dependent on the existence of some other entity type for its primary key– For example, Next_of_Kin, Appointment, ... (see next slide)

– Has no primary key of its own

90

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Weak Entities: in Diagrams

• Note the total participation (why?)

Employee Dependent

0..*

has1..1 Weak entities

NameEmployee_id[PK]

91

Client Appointmentmade

1..1 0..*

Weak entities

DateTime

Client_id[PK]

Summary

• ER model and diagrams

– Entities, attributes and relationships

• Types of relationships

C di li– Cardinality: one‐to‐one, one‐to‐many, many‐to‐one, many‐to‐many

– Participation: total / partial

92

CO7101 Java & Databases

Normalization: When There Is

CO7101 Java & Databases 93

Normalization: When There Is Something Fishy In Your Databases

Dr. Stuart Kerrigan

Revision : The components of a DB

Database

Data

a abaseManagement

System

Limitations of FFDBs

Flat file databases are suitable for storage tasks if data is simple or if there is not tootasks if data is simple, or if there is not too much of it.

If data stored is too complex, then the flat file database breaks down ‐ it exhibits a number of anomalies.

Example DatabasesSUPPLIER SUPPLIER

ADDRESSSUPPLIERPHONE

GOODSSUPPLIED

DATESUPPLIED

INVOICENUMBER

Viglen 23 Main St. 234345 2 586 PCs 23/3/97 3456483Opus 5 High St. 343434 6 486 PCs 12/12/96 4566578Opus 5 High St. 343434 1 printer 3/4/97 4566683Viglen 23 Main St. 234345 4 586 PCs 12/1/97 3456210Opus 5 High St. 343434 2 486 PCs 12/3/97 4566602

STUDENT STUDENT. No. COURSE LECTURER DEPT. ROOM TIMESmith, A. 765432 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Smith, A. 765432 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Bloggs, F. 776829 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 Chem1 Dr. Bell Chem CLT 12.00

TITLE AUTHOR PUBLISHER YEAR ISBN PRICEInformation Technology Smith & Jones Collins 1990 1-23445-345 £20.00Information Technology Smith & Jones Collins 1996 1-23445-319 £25.00Databases for Dummies Bloggs Longmans 1993 2-34542-422 £15.00Spreadsheets for Idiots Macpherson Collins 1994 4-34589-445 £18.00

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Update Anomaly

If data appears more than once in the database, then if one item of the data is altered, we must alter all the instances of that data.

Example ‐ Update Anomaly

SUPPLIER SUPPLIERADDRESS

SUPPLIERPHONE

GOODSSUPPLIED

DATESUPPLIED

INVOICENUMBER


SUPPLIER SUPPLIERADDRESS

SUPPLIERPHONE

GOODSSUPPLIED

DATESUPPLIED

INVOICENUMBER


Insertion Anomaly

If new information is available, we may not be able to enter the data until we have data for all fields.

Example ‐ Insertion Anomaly

STUDENT STUDENT. No. COURSE LECTURER DEPT. ROOM TIMESmith, A. 765432 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Smith, A. 765432 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Bloggs, F. 776829 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 Chem1 Dr. Bell Chem CLT 12.00

STUDENT STUDENT. No. COURSE LECTURER DEPT. ROOM TIMESmith, A. 765432 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Smith, A. 765432 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Bloggs, F. 776829 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 Chem1 Dr. Bell Chem CLT 12.00. Chem2 Dr. Clapper Chem

Deletion Anomaly

If we delete some information from the database, we may accidentally remove additional data which we wish to keep.

Example ‐ Deletion Anomaly

STUDENT STUDENT. No. COURSE LECTURER DEPT. ROOM TIMESmith, A. 765432 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Smith, A. 765432 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Bloggs, F. 776829 CO1005 Dr. Solanki CompSci PH LTA 1.00gg pBloggs, F. 776829 Chem1 Dr. Bell Chem CLT 12.00

If we delete Bloggs from the Chem1 course we lose our only record that Dr. Bell teaches this class in the Chem Department Room CLT at 12.00.

Not very intelligent.

18

Functional Dependency

All these anomalies occur because some fields are functionally dependenton one another.

ll d h i D K i ille.g. all records showing Dr. Kerrigan will show his Department as Computer Science, and so on.


• A property that exists between fields

– that the value in one field determines the value that can be contained in the other field

• E g if you know the value of the first attribute• E.g. if you know the value of the first attribute you can find the value of a second attribute

Example of FD

A B

If I know the value of A I can find the value of B

Real Life Example of FD

A B

StudentID StudentName

If I know the StudentID I can find the corresponding StudentName


A B

StudentID StudentName

Date of Birth

If I know the StudentID I can find the corresponding StudentName and the corresponding Date Of Birth


A B

StudentID[PK]

StudentName

Date of Birth

In good database design all non-key fields should be dependant solely on all parts of the primary key.

19

Composite Primary KeysClientID[PK] Date of

BirthPropertyID

[PK]

ClientID[PK]

Comments

In good database design all non-key fields should be dependant solely on all parts of the primary k

PropertyID[PK]

Transitive Dependency

A B

TransactionID CustomerName

If I know the TransactionID I can find the Customer’s Name. Once I know the Customer’s Name I can find the SalesRep’s Name

SalesRep


A B

TransactionID CustomerName

If I know the TransactionID I can find the Customer’s Name. Once I know the Customer’s Name I can find the SalesRep’s Name

SalesRep

The Solution ‐Multiple Tables

We must extract some of the data fields from the list (or table) and create a second table (or more).

Our application must now be able toOur application must now be able to handle multiple tables, and perform queries etc. across multiple tables.

Converting a Database

If we have an existing flat file database, we can convert it into a well‐behaved relational database via a step‐by‐step process known as normalisation.

Normalisation

First normal form according to Codd ‐

All fields must contain atomic data.

Codd defines an atomic value as one that "cannot be decomposed into smaller pieces by the DBMS (excluding certain special functions).”

20

Example ‐ 1NF According to CoddAre fields atomic?

Name[PK]

Office PhoneNumber1

PhoneNumber2

PhoneNumber3

Dr. Stuart Kerrigan F25 3333 4452 34421

Prof. Klaus Himmelheim

D22 211 NULL NULL

M P t V k ECTO1 3332 3432 NULL

Why is this example NOT in 1NF?

Mr. Peter Venkman ECTO1 3332 3432 NULL

Example ‐ 1NF According to CoddAre fields atomic?

Title[CPK]

FirstName[CPK]

Surname[CPK]

Office PhoneNumber1

PhoneNumber2

PhoneNumber3


Prof. Klaus Himmelheim D22 211 NULL NULL

Name was not atomic – could be further decomposed.

Note composite primary key.


Example ‐ 1NF

STUDENT STUDENT. No. COURSE LECTURER DEPT. ROOM TIMESmith, A. 765432 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Smith, G. 765432 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Bloggs, T. 776829 CO1005 Dr. Solanki CompSci PH LTA 1.00gg pBloggs, F. 776829 Chem1 Dr. Bell Chem BEN LT5 1.00

INITIAL STUDENT. No. COURSE LECTURER DEPT. ROOM TIMEA. 765432 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00G. 765432 CO1005 Dr. Solanki CompSci PH LTA 1.00F. 776829 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00T. 776829 CO1005 Dr. Solanki CompSci PH LTA 1.00F. 776829 Chem1 Dr. Bell Chem BEN LT5 1.00

SURNAMESmithSmithBloggsBloggsBloggs

These 3 columns repeat as they are storing the same information

Repeating Columns

PhoneNumber1

PhoneNumber2

PhoneNumber3

3333 4452 34421

211 NULL NULL

3332 3432 NULL

Remove Repeating Columns

Example ‐ 1NF According to Date

Title[CPK]

FirstName[CPK]

Surname[CPK]

Office PhoneNumber1

PhoneNumber2

PhoneNumber3


Prof. Klaus Himmelheim D22 211 NULL NULL


StaffID[PK]

Title FirstName

Surname Office

1 Dr. Stuart Kerrigan F25

2 Prof. Klaus Himmelheim D22

3 Mr. Peter Venkman ECTO1

PhoneNumber [PK]

StaffID[FK]

3333 1

4452 1

34421 1

211 2

3332 3

3432 3

Phone Staff

Normalisation

Second normal form ‐

• Must be 1NF.

• Automatically 2NF if no composite• Automatically 2NF if no composite primary key.

• Each nonkey attribute in table must be functionally dependent upon the whole primary key.

21

Example ‐ 2NFViewing

ClientNo[Comp PK]

PropertyNo[Comp PK]

ViewDate Comment FirstName LastName City

CR56 PA14 24‐May‐01 too small Annie Bradock Detroit

CR56 PG36 28‐Apr‐01 NULL Annie Bradock Edinburgh

CR56 PG4 26‐May‐01 NULL Annie Bradock Londony

CR62 PA14 14‐May‐01 no dining room

John Wayne Detroit

CR76 PG4 20‐Apr‐01 too remote Ivor Taper London

• Note the composite primary key (i.e. key consists of 2 fields)

• Each nonkey attribute in table must be functionally dependent upon the entire primary key.

• Is this so?

Example ‐ 2NFClientNo[Comp PK Foreign Key]

PropertyNo[Comp PKForeign Key]

ViewDate Comment

CR56 PA14 24‐May‐01 too small

CR56 PG36 28‐Apr‐01 NULL

CR56 PG4 26‐May‐01 NULL

CR62 PA14 14‐May‐01 no dining room

ClientNo[PK]

FirstName LastName

CR56 Annie Bradock

CR62 John Wayne

CR76 Ivor Taper

CR76 PG4 20‐Apr‐01 too remote

PropertyNo[PK]

City

PA14 Detroit

PG36 Edinburgh

PG4 London

Now in 2nd Normal Form

Normalisation

Third normal form ‐

• Must be 2NF.

• All the non‐key fields must be dependent on the primary key.

Example ‐ 3NFOrderNo[PK]

Customer ContactPerson

Total

1 Acme Dave £20

2 StuCorp Fred £20000

3 Acme Dave £15

4 Acme Dave £123

•OrderNo serves as the primary key.•Customer and total amount are dependent on the order number ‐‐ this data is specific to each order.•However, the contact person is dependent upon the customer.•There is really a 1‐1 relationship between Customer and Contact Person.

5 StuCorp Fred £0.50

Example ‐ 3NFOrderNo[PK]

Customer Total

1 Acme £20

2 StuCorp £20000

3 Acme £15

4 Acme £123

Customer[PK & Foreign Key]

ContactPerson

Acme Dave

StuCorp Fred

•Create tables to represent relations ‐ a 1‐1 relationship between Customer and Contact Person.

4 Acme £123

Example ‐ 3NF

INITIAL Student. No. pk COURSE LECTURER DEPT. ROOM TIMEA. 765432 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00A. 765432 CO1005 Dr. Solanki CompSci PH LTA 1.00F. 776829 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00F 776829 CO1005 D S l ki C S i PH LTA 1 00

SURNAMESmithSmithBloggs

l F. 776829 CO1005 Dr. Solanki CompSci PH LTA 1.00F. 776829 Chem1 Dr. Bell Chem BEN LT5 1.00

BloggsBloggs

22

Example ‐ Converting to 3NFSTUDENT STUDENT. No. COURSE LECTURER DEPT. ROOM TIMESmith, A. 765432 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Smith, A. 765432 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 CO1019 Dr. Kerrigan CompSci BEN LT5 2.00Bloggs, F. 776829 CO1005 Dr. Solanki CompSci PH LTA 1.00Bloggs, F. 776829 Chem1 Dr. Bell Chem BEN LT5 1.00

COURSELECTURERINITIAL STUDENT NoSURNAME

STUDENT. No. COURSE765432 CO1019765432 CO1005776829 CO1019776829 CO1005776829 Chem1

COURSE ROOM TIMECO1019 BEN LT5 2.00CO1005 PH LTA 1.00Chem1 BEN LT5 1.00

CO1019Dr. KerriganCO1005Dr. SolankiChem1Dr. Bell

INITIAL STUDENT. No.A 765432F 776829

SURNAMESmithBloggs

2NF and 3NF

• Difference between the second and third normal forms of a normalizednormalized database?– "The key,

– the whole key,

– and nothing but the key,

– so help me Codd."

2NF

3NF

Beyond 3NF

Boyce‐Codd normal form (BCNF)

Raymond F. Boyce and Codd(1974)

Every non‐trivial functional dependency in the table is a dependency on a superkey

Fourth normal form (4NF)

Fagin (1977)

Every non‐trivial multivalued dependency in the table is a dependency on a superkey

Every non‐trivial join

Fifth normal form (5NF) Fagin (1979)dependency in the table is implied by the superkeys of the table

Domain/key normal form (DKNF)

Fagin (1981)

Every constraint on the table is a logical consequence of the table's domain constraints and key constraints

Sixth normal form (6NF)Chris Date, Hugh Darwen, and Nikos Lorentzos (2002)

Table features no non‐trivial join dependencies at all (with reference to generalized join operator)

Beyond 3NF• First normal form (1NF) ‐ Codd (1970), Date (2003) ‐ Table faithfully

represents a relation, data is atomic and has no “repeating groups”• Second normal form (2NF) ‐ Codd (1971) ‐ No non‐prime attribute in the

table is functionally dependent on a part (proper subset) of a candidate key

• Third normal form (3NF) ‐ Codd (1971) ‐ Every non‐prime attribute is non‐transitively dependent on every key of the table

• Boyce‐Codd normal form (BCNF) ‐ Boyce and Codd (1974)‐ Every non‐trivial functional dependency in the table is a dependency on a superkeytrivial functional dependency in the table is a dependency on a superkey

• Fourth normal form (4NF) ‐ Fagin (1977) ‐ Every non‐trivial multivalueddependency in the table is a dependency on a superkey

• Fifth normal form (5NF) ‐ Fagin (1979) ‐ Every non‐trivial join dependency in the table is implied by the superkeys of the table

• Domain/key normal form (DKNF) ‐ Fagin (1981) ‐ Every constraint on the table is a logical consequence of the table's domain constraints and key constraints

• Sixth normal form (6NF) ‐ Date, Darwen, and Lorentzos (2002) ‐ Table features no non‐trivial join dependencies at all (with reference to generalized join operator)

SUMMARY

–Flat file databases can handle only simple and small scale data, otherwise anomalies occur

–Relational databases can handle complex–Relational databases can handle complexand large amounts of data

–Normalisation is used to ensure efficient relationships

Relationships & Functional Dependencyp y

Dr. Stuart Kerrigan

23

A Simple Binary Relationship

• People own many houses.

• Some people own no houses.

• Some houses are unowned.

• Some houses have many people in them.


• People own many houses.

• Some people own no houses.

• Some houses are unowned.



• People can live in many houses.

• Some people live in no houses.

S h• Some houses are empty.



• People can live in many houses.

• Some people live in no houses.

S h• Some houses are empty.


A Simple? Relationship

• Some staff manage 1 or more staff members.

• Some staff do not manage other staff membersother staff members.

• A staff member has at most one manager

A Simple? Relationship

• Management staff manage 1 or more staff members.

• Some staff do not manage other staff members

manages

other staff members.

• A staff member has at most one manager

24


• A property that exists between fields

– that the value in one field determines the value that can be contained in the other field

• E g if you know the value of the first attribute• E.g. if you know the value of the first attribute you can find the value of a second attribute

Example of FD

A B

If I know the value of A I can find the value of B


A B

StudentIDStudent Name

If I know the StudentID I can find the corresponding StudentName


A B

StudentIDStudent Name

Date of Birth

If I know the StudentID I can find the corresponding StudentName and the corresponding Date Of Birth


A B

StudentID[PK]

StudentName

Date of Birth

In good database design all non-key fields should be dependant solely on all parts of the primary key.

Composite Primary KeysClientID[PK] Date of

BirthPropertyID

[PK]

ClientID[PK]

Comments

In good database design all non-key fields should be dependant solely on all parts of the primary k

PropertyID[PK]

25


A B

TransactionID

Customer Name

If I know the TransactionID I can find the Customer’s Name. Once I know the Customer’s Name I can find the SalesRep’s Name.

SalesRep


A B

TransactionID

CustomerName

If I know the TransactionID I can find the Customer’s Name. Once I know the Customer’s Name I can find the SalesRep’s Name.

SalesRep


SQL 1:


147

Simple Data Definition and Select Statements

Dr. Stuart Kerrigan

SQL Components: DDL, DML, & DCL

• SQL is a transform‐oriented language

• SQL is a non‐procedural language: specify what info you require rather than how you access the data

• SQL is a very large and powerful language, but every type of SQL statement falls within one of three main categories (or sub‐languages):

• Data Definition Language (DDL) for creating a DB, defining & controlling g g ( ) g , g gaccess to data

e.g. CREATE, DROP, ALTER

• Data Manipulation Language (DML) to access a DB by retrieving and updating data

e.g. SELECT, INSERT, UPDATE, DELETE

• Data Control Language (DCL) for administering a DB

e.g. GRANT, DENY, USE

148

SQL ‐ Structured Query Language

• SQL was developed at IBM around 1975...• Structured programming?No! ‐ Structured English Query Language (from 'SEQUEL') which implements relational algebra

• SQL is a declarative language ‐ says what not howSQL is a declarative language says what not how• SQL is an abstract & portable interface to RDBMS• Different versions of SQL slightly different syntax• We use mySQL• Only standard db language to gain wide acceptance

149

SQL Syntax• SQL uses reserved keywords & user‐defined names

CREATE TABLE Staff ( StaffNo INTEGER, Salary FLOAT,

Lname VARCHAR(20) );

• This means create a table called staff with the following fields:– StaffNo as an Integer– Salary as a FlatSalary as a Flat– Lname as a text field with 20 charactersINSERT INTO Staff VALUES (32, 25000.0, 'Smith');

• This means insert into our staff table a row with the following fields:– StaffNo of 32– Salary of 25000.0– Last name of 'Smith'

150

26


CREATE TABLE Staff ( StaffNo INTEGER, Salary FLOAT,Lname VARCHAR(20) );INSERT INTO Staff VALUES (32, 25000.0, 'Smith');

• By convention, keywords are upper‐case, though most SQL dialects are case‐insensitive;

• User‐defined names must be entered exactly as in tablesd i l d i i l (' ')• Text data is enclosed using single quotes (' ')

• Round brackets () are used to group related items• Commas , separate items in a list• Statements are terminated with a semicolon (';')• | indicates choice; literals: non‐numeric require single quotes,

e.g., VALUES('Bob',4); [] indicates optionality

151

Relational Tables Can AnswerMany Queries

Student Enrolment Course

152

How many courses are there & what are their names?Which students are enrolled for Java? How many students take 3 or more courses?

Data Definition Language (1)• The SQL syntax for CREATE TABLE isCREATE TABLE table_name (

Column1name data_type_for_column_1,

Column2name data_type_for_column_2,... )

Column Type Description Syntax

153

yp p y

int Accepts integer values only tinyint, int

float Accepts float values only float

boolean Accepts a TRUE or FALSE value boolean

varchar Accepts any symbol, character, or number

varchar(char limit

value), for example

varchar(20) is

string of length 20

date Date (YYYY‐MM‐DD), e.g. 2009‐02‐23 date

Data Definition Language

• How would you create the following table?• First decide what type of field to use for each field• StaffNo – this is obviously an integer• Fname, Lname, Position are text fields• Salary – this could be debatable. Let's make it a float.

StaffNo Fname Lname Position Salary

Salary this could be debatable. Let s make it a float.CREATE TABLE Staff (StaffNo INTEGER, Fname VARCHAR(20), Lname VARCHAR(20), Position VARCHAR(20), Salary FLOAT);

• mySQL description of this table is as follows:‐

154

Data Definition Language

• Forgot the domains of your table?• Use the command

DESCRIBE table_name• e.g. DESCRIBE Staff;

155

Built‐in Data Types (Domains) inMySQL

• SQL supports many data types (vendors often also have own dialects):– CHARACTER (CHAR), CHARACTER VARYING (VARCHAR)– NUMERIC, DECIMAL (DEC), INTEGER (INT), SMALLINT– FLOAT, REAL, DOUBLE PRECISION– DATE, TIME, TIMESTAMP– BOOLEAN, BIT– BINARY LARGE OBJECT (BLOB), etc.

• Some types have an associated size . e.g. CHAR(5)

156

27


CREATE TABLE Staff ( StaffNo INTEGER,Salary FLOAT, Lname VARCHAR(20));

• This means create a table called staff with the following fields:– StaffNo as an Integer– Salary as a Flat– Lname as a text field with 20 charactersa e as a e e d 0 c a ac e s

• Now we want to add data to our table.INSERT INTO Staff VALUES (32, 25000.0, 'Smith');

• This means insert into our staff table a row with the following fields:– StaffNo of 32– Salary of 25000.0– Last name of 'Smith'

157

SQL Syntax


222 Head Honcho CEO 35000

322 Mark Jones Manager 20000

261 Julie Walters Director 40000

260 Julie Walters Tax Shelter 20000

Staff

• How would you insert the values into the table?– INSERT INTO Staff VALUES (222,'Head','Honcho','CEO',35000);– INSERT INTO Staff VALUES (322,'Mark','Jones','Manager',35000);– INSERT INTO Staff VALUES

(261,'Julie','Walters','Director',40000);– INSERT INTO Staff VALUES (260,'Julie','Walters','Tax

Shelter',20000);– INSERT INTO Staff VALUES (555,'Dogollan','Body','Cleaner',500);– INSERT INTO Staff VALUES (444,'Trinity','Wells','Porter',200);

158

555 Dogollan Body Cleaner 500

444 Trinity Wells Porter 200

SQL Syntax• Suppose we don’t know all the information?

– e.g. we know a person’s lastname, position and salary but not their staff number or first name?

INSERT INTO Staff (Lname, Position, Salary) VALUES ('Peters','Cleaner',30);

• Leaves the unknown fields as NULL. Can put these in later…


159








NULL NULL Peters Cleaner 30

Simple Queries Using SELECTSELECT * FROM Staff;




Staff

160

•Here, asterisk * acts as a 'wild card'•that means SELECT all the fields FROM the staff table

•Outputs a table (so SELECT is a closed operation)





Simple Queries Using SELECT•The SELECT statement retrieves data and formats output•SELECT is the most frequently used SQL statement•Performs relational algebra's selection, projection and join operations in a single statement

SELECT * FROM Staff;•In English this means select all the rows from the staff table.

161

SELECT

SELECT fields‐list FROM table‐listWHERE condition;

• tables‐list ‐ A list of table names you wish to select from.• fields‐list‐A list of fields from the tables in tables‐list; can also

if di i ( d li ) ll (*)specify distinct (no duplicates) or all (*)• condition– filters rows subject to some condition

SELECT Fname FROM Staff;

SELECT Fname, Lname FROM Staff WHERE Salary > 15000;

162

28

Selecting Specific Columns•Specific columns can be output by giving their names:

SELECT Fname FROM Staff;Fname

Head

Mark

163

•In English this means:‐•Select the first names (Fname) field for all the rows FROM the staff table

Mark

Julie

Julie

Dogollan

Trinity

Selecting Specific Columns•Specific columns can be output by giving their names:

SELECT Lname, Position, Salary FROM Staff;Lname Position Salary

Honcho CEO 35000

Jones Manager 20000

164

NB. must have a comma (',') between column names•In English this means:‐

•Select the last names (Lname), positions (Position) and Salaries (Salary) fields of all the rows from the staff table

Jones Manager 20000

Walters Director 40000

Walters Tax Shelter 20000

Body Cleaner 500

Wells Porter 200

Selecting Specific Columns•Use WHERE to specify a condition:

SELECT Fname, Lname, Salary FROM StaffWHERE Salary > 15000;

165

•In English means:‐•Select the first names (Fname), positions (Position) and Salaries (Salary) for all the rows FROM the staff table WHERE the salary is more than 15000

Selecting Distinct Rows•Use DISTINCT to get only one occurrence of values

SELECT DISTINCT Fname, Lname FROM Staff;Fname Lname

Head Honcho

Mark Jones

Julie Walters

166

•In English this means:‐•Select unique occurrences of the first names (Fname) and last names (Lname) FROM the staff table (i.e. no 2 Julie Walters)

•What about this query? How many rows would we get?SELECT DISTINCT Fname, Salary FROM Staff;

Dogollan Body

Trinity Wells

Selecting Specific Rows & Columns•comparison operators: < less than> greater than= equal to <= less than or equal to

167

>= greater than or equal to != not equal to lesser than or greater than

also use AND, OR and NOT

Selecting Specific Rows & Columns

•can also test for range (BETWEEN, NOT BETWEEN), SELECT Fname, Lname, Salary FROMStaff WHERE Salary BETWEEN 0 AND 10000;

•set membership (IN ('Manager'), NOT IN), •pattern match

SELECT * from Staff WHERE Lname LIKE 'W%';

168

SELECT from Staff WHERE Lname LIKE W% ;SELECT * from Staff WHERE Lname NOT LIKE 'W%';

•whether null (IS NULL, IS NOT NULL)•Condition 'Salary > 20000' is called a predicate•For each row, if predicate is true, row is output

29

Computed/Derived Fields

•Can also compute our own fields•MonthlySalary is a computed field – it is Salary divided by 12

SELECT Fname,Lname,Salary/12 as MonthlySalaryFROM Staff;

•FullName is a computed field concatenating two fields.SELECT concat(Fname ' ' Lname) as FullName

169

SELECT concat(Fname, ,Lname) as FullName FROM Staff;

•When new fields are calculated we can name them using AS


170


171

Building Up Complex Predicates

• Predicates evaluate to either true or false• Predicates can be combined using AND, OR, and NOT• Use brackets to avoid ambiguity• The next two statements are different:

1.SELECT * FROM Staff WHERE (Position = 'Manager') ORWHERE (Position = Manager ) OR(Position = 'Assistant' AND Salary > 10000);

2.SELECT * FROM Staff WHERE(Position = 'Manager' OR Position = 'Assistant‘)AND NOT (Salary <= 10000);

• In each case, whole WHERE clause is true or false• NULL is not equivalent to '' or <>, can't test equality; use IS

172

Other Types of Predicate

• Other predicates include BETWEEN, IN, and LIKE

• But they still evaluate to either true or falseSELECT * FROM Staff WHERE (Salary BETWEEN 10000 AND 40000) AND (Position IN ('CEO','Director','Cleaner')) AND (Fname LIKE 'H_ _ _' OR Lname LIKE 'W%');

• '_' matches exactly one character

• '%' matches zero or more characters

• So what does this query match?

173

Answer– SELECT * FROM Staff WHERE (Salary BETWEEN 10000 AND 40000) AND (Position IN ('CEO','Director','Cleaner')) AND (Fname LIKE 'H_ _ _' OR Lname LIKE 'W%');

– SELECT all the fields FROM the staff table WHERE the salary is between 10000 and 40000 and the position is either CEO, Director or Cleaner and the firstname begins with H and has 3 characters following it or the lastname begins with W. 174

30

Conclusion

• SQL is the standard query language for RDBMS• Three main categories of SQL

– DDL, Data Definition Language– DML, Data Manipulation Language DCL Data Control Language– DCL, Data Control Language

• CREATE, ALTER and DROP tables using DDL.• SELECT belongs to DML• SELECT retrieves & displays data from the database

• We continue to explore DML


175


SQL 2:


176

More on SELECT then UPDATE, DELETE

Dr. Stuart Kerrigan

Previously on CO1019:

• Can CREATE tables in a mySQL database

• Can INSERT INTO tables in a mySQL database

• Can use SELECT to– Retrieve data from all the rows and columns (whole table)

SELECT * FROM Staff;


177

– Retrieve data from all the rows and select columns

SELECT Fname, Lname FROM Staff;– Retrieve data from select rows and columns

SELECT Fname, Lname FROM Staff WHERE Salary > 10000;

– Compute derived field valuesSELECT Salary/12 as monthySal FROM Staff;

In this lecture you will learn

• Calculate aggregate derived data

• GROUP BY and ORDER BY in SELECT statements

• Modify row data


178

• Delete row data

• Delete entire tables

• NULL values in databases

• How to combine query results using set unions

SQL Aggregate Functions

• We do not want to just retrieve data

• We also want to summarise data

• Use in SELECT list and HAVING clause only

• Aggregate functions compute summarization (or aggregation) of data & return a value


179

aggregation) of data & return a value

• DISTINCT eliminates duplicates first

• Aggregate functions over a column – SUM – sums column values (numeric fields only)

– AVG – averages column values (numeric fields only)

– MIN – gives min column value

– MAX – gives max column value

– COUNT – gives number of values in column

SUM, MIN, MAX, AVG• Find the minimum, maximum, average and sum of staff salarySELECT MIN(salary) AS minSalary,MAX(salary) AS maxSalary,AVG(salary) AS avgSalary, SUM(salary) AS sumSalary,CO ( l ) S S l


180

COUNT(salary) AS countSalaryFROM Staff;

31

GROUP BY

• Aggregate functions help us to summarise the whole column(s) of data into one row.

• Sometimes we want to group data before applying aggregate functions

– This gives us 'subtotals' rather than 'overall total'


181

• GROUP BY is used to achieve that

• Closely tied to SELECT; can only have column names, aggregate functions, constants, a combination of these

• All columns in SELECT list must appear in GROUP BY clause unless they're in an aggregate function

• WHERE condition applied before GROUP BY

GROUP BY ‐ Example

• Find the total salaries of each person on payroll by adding salaries from different jobs. Group by their first name.

SELECT Fname, Lname, SUM(Salary) AS TotalSalary FROM Staff GROUP BY Fname, Lname;


182

MoreStaff

HAVING• Use with GROUP BY to restrict output; filters groups rather

than rows (WHERE); condition has aggregate fnSELECT branchNo, Count(staffNo) AS myCount, SUM(salary) AS mySum FROM MoreStaff GROUP BY branchNo HAVING COUNT(staffNo)>1;

StaffNo Fname Lname Position Sex DOB Salary BranchNo

SA9 Mary Howe Assistant F 19 Feb 70 9000 B007

QuerybranchNo myCount mySum

B003 3 54000

B005 2 120000

SA9 Mary Howe Assistant F 19‐Feb‐70 9000 B007

SG14 David Ford Supervisor M 24‐Mar‐58 18000 B003

SG37 Ann Beech Assistant F 11‐Oct‐60 12000 B003

SG5 Susan Brand Manager F 03‐Jun‐40 24000 B003

SL21 John White Manager M 01‐Oct‐45 30000 B005

SL41 Julie Lee Assistant F 13‐Jun‐65 90000 B005

SELECT – Group By

SELECT fields‐listFROM table‐listWHERE condition;GROUP BY columnList [HAVING condition]ORDER BY columnList

• GROUP BY filters groups of rows…• Work out aggregate functions for each group in grouped

columns


184

SELECT – Order By

SELECT fields‐listFROM table‐listWHERE condition;GROUP BY columnList [HAVING condition]ORDER BY columnList

• ORDER BY sorts results ‐ can be ASCending or DESCendingORDER BY sorts results can be ASCending or DESCending• SELECT * FROM StaffORDER BY salary DESC;SELECT * FROM StaffORDER BY Fname ASC;SELECT * FROM Staff ORDER BY Lname ASC, Fname ASC, Position DESC;


185

A

Z

Z

A

UPDATE Queries

UPDATE table‐listSET field1 = value1

field2 = value2 …WHERE condition; (WHERE is optional)

UPDATE Staff SET Fname ='Dilbert';S ll Fi N 'Dilb ' i h S ff blSets all First Names to 'Dilbert' in the Staff table.

UPDATE Staff SET Position='Chief Executive Officer' WHERE Position = 'CEO';

Sets Positions of 'CEO' to 'Chief Executive Officer' in the Staff table.

UPDATE Staff SET Salary = 10000 WHERE Salary < 10000;

Sets Salary to 10000 where Salary is less than 10000 in the Staff table.


186

32

UPDATE Queries• Changing specific values in a table:

UPDATE Staff SET Salary = 1.05*Salary

WHERE Position = 'Director';

UPDATE the STAFF table by multiplying the salary by 1.05 where the Position is Director


187

DELETE Queries

DELETE FROM table‐listWHERE condition;

• Deleting all rows of a table:DELETE FROM Staff;

• Deleting specific rows of a table:


188

• Deleting specific rows of a table:DELETE FROM Staff WHERE Fname = 'Julie' AND Lname = 'Walters';

• Completely removing a table is a DDL (data definition language) operation:

DROP TABLE Staff;

Why Do DB Systems Allow NULLs ?

• A NULL value can be used to represent several situations:

• Don't care; Don't know; Don't know yet; Used to know!

• SQL has special rules and logic to handle NULLs:SELECT * FROM Staff WHERE Fname IS NULL;

• NB. WHERE Colname = 'NULL' does not work ! Can't test


189

NB. WHERE Colname NULL does not work ! Can t test equality on something that doesn't exist! IS is not the same as =

• Can also say: WHERE Colname IS NOT NULL

• NULLs can be useful, difficult, or dangerous

• Use NULLs wisely!

A Null Example

StaffNo Fname Lname Position Salary Room

222 Head Honcho CEO 35000 F5

322 Mark Jones Manager 20000 F30

Staff_With_Rooms

322 Mark Jones Manager 20000 F30

261 Julie Walters Director 40000 F1

260 Julie Walters Tax Shelter 20000 NULL

555 Dogollan Body Cleaner 500 NULL

444 Trinity Wells Porter 200 Cellar

Combining Results Tables

• Requirements: tables need to have same structure so they're union‐compatible

• Sometimes its useful to be able to combine query results using set operations:

R ∩ S R - SR U S


191

(a) Union (b) Intersection (c) Difference (Excep

R

S S S

R R

Set Operations in SQL

• Syntax:

(SELECT ...) UNION (SELECT ...);• For set operations, the tables must be union‐compatible

– i.e. have the same number and types of columns

• (SELECT city FROM Branch WHERE city IS NOT NULL) UNION (SELECT city FROM PropertyForRent WHERE city


192

UNION (SELECT city FROM PropertyForRent WHERE city IS NOT NULL);

33

Remember this data?




Staff






Union‐Compatible?


523 Redwood Mark CEO 20000

211 Bilbo Baggins Hobbit 12000


Staff2

CREATE TABLE Staff2 (StaffNo INTEGER, Fname VARCHAR(20), Lname VARCHAR(20), Position VARCHAR(20), Salary FLOAT);

INSERT INTO Staff2 VALUES (222,'Redwood','Mark','CEO',20000),(322,'Bilbo','Baggins','Hobbit',12000),(260,'Julie','Walters','Tax Shelter',20000);

(SELECT * FROM Staff) UNION (SELECT * FROM Staff2);


Results of our UnionStaffNo Fname Lname Position Salary







523 Redwood Mark CEO 20000

211 Bilbo Baggins Hobbit 12000

Results of our Union

Union‐Compatible?

StaffNo Fname Lname Position Salary Branch

123 Gilbert Laycock Engineer 35000 ENG1

212 Lenny Henry Morale Officer 20000 SCO1

260 Julie Walters Tax Shelter 20000 FRA1

Staff3

CREATE TABLE Staff3 (StaffNo INTEGER, FnameVARCHAR(20), Lname VARCHAR(20), Position VARCHAR(20), Salary FLOAT, BRANCH VARCHAR(20));

INSERT INTO Staff3 VALUES (123,'Gilbert','Laycock','Engineer',20000, 'ENG1'),(322,'Lenny','Henry','Morale',20000),(260,'Julie','Walters','Tax Shelter',20000);


Union‐Compatible?

StaffNo Fname Lname Position Salary Branch

123 Gilbert Laycock Engineer 35000 ENG1

212 Lenny Henry Morale Officer 20000 SCO1

260 Julie Walters Tax Shelter 20000 FRA1

Staff3


Won't work – why?

(SELECT * FROM Staff) UNION (SELECT StaffNo, Fname, Lname, Position, Salary FROM Staff3);

34

Union ExampleR U S

(a) Union (b) Intersection (c) Difference (Exce

R

S S S

R R

• Covered unions, but what about Intersections and Differences?

( ) ( ) ( ) (

Intersect and ExceptR U S

(a) Union (b) Intersection (c) Difference (Exce

R

SS S

R R

• Covered unions, but what about Intersections and Differences.

• SQL keywords are INTERSECT and EXCEPT e.g.

(SELECT * FROM Staff) INTERSECT (SELECT * FROM Staff2);(SELECT * FROM Staff) EXCEPT(SELECT * FROM Staff2);

• Sadly not supported in MySQL. There are workarounds on the internet (use Google) – but these use subqueries!

( ) ( ) ( ) (

Intersect Example

SELECT DISTINCT * FROM Staff WHERE EXISTS (SELECT * FROM Staff2 WHERE Staff.StaffNo = Staff2.StaffNo AND Staff.Fname = Staff2.Fname AND Staff.Lname = Staff2.Lname AND Staff.Position = Staff2.Position AND Staff Salary = Staff2 Salary);Staff.Salary = Staff2.Salary);

SELECT DISTINCT * FROM Staff WHERE NOT EXISTS (SELECT * FROM Staff2 WHERE Staff.StaffNo = Staff2.StaffNo AND Staff.Fname = Staff2.Fname AND Staff.Lname = Staff2.Lname AND Staff.Position = Staff2.Position AND Staff.Salary = Staff2.Salary);

More on (simpler?) subqueries next time!

Conclusion

• Now understand complete SELECT syntax

• Can use aggregate functions

• UPDATE and DELETE queries

• Understand when to use NULLs in database• Understand when to use NULLs in database design.

• Can now perform simple UNIONS between tables


202


SQL 3:


203

Subqueries and Multiple Tables

Dr. Stuart Kerrigan

Previously on CO1019:

• CREATE tables, INSERT data into table and SELECT data out of table

• Use Aggregate functions

• UPDATE data and DELETE data from table– ALL ON ONE TABLE ONLY!


204

• Create a Union between two identical queries of different tables

35








401 Taffy Truman Manager 30000

322 Gareth Whirlwind Manager 32500

Using Subqueries ‐ Nested SELECTs

• If we know that a SELECT statement will produce a single value or row we can use this value directly in a simple predicate.

• This subquery must appear in brackets (); ORDER BY can't appear in a subquery; most subqueries can't have more than 1 table in SELECT list

• Can appear after a relational operator, function or set operator in WHERE SELECT & HAVING clauses

CO7101: Java & Databases For Bioinformatics 206

WHERE, SELECT & HAVING clauses

• Example: find all members of staff who earn more than the managers:

SELECT * FROM Staff WHERE Salary > (SELECT Salary FROM Staff WHERE Position ='Manager');

Doesn't work when we introduce multiple managers!

Subqueries That Give a List of Values

• If the SELECT statement is expected to produce a list of values, we can use the IN, ANY, ALL or EXISTS keywords to operate on the list.

• Example: find those members of staff who are not managers but earn more than anymanagers:SELECT * FROM Staff WHERE Position <> 'Manager'


gAND Salary > ANY (SELECT Salary FROM Staff WHERE Position = 'Manager');

ANY: Predicate is true if it matches ANY value in the liste.g. statement is true if staff is not a manager and has a higher salary than any manager.

SELECT * FROM Staff WHERE Position <> 'Manager' AND Salary > SOME (SELECT Salary FROM Staff WHERE Position ='Manager');

SOME: Synonym for any (i.e. you can use SOME or ANY interchangably)


SELECT * FROM Staff WHERE Position <> 'Manager' AND Salary > ALL (SELECT Salary FROM Staff WHERE Position ='Manager');ANY: Predicate is true if it matches ALL value in the liste.g. statement is true if staff is not a manager and has a higher salary than ALL the managers.


• SELECT * FROM Staff WHERE position IN ('Manager', 'Supervisor');IN: Predicate is true if the test element is in the list; (i.e. if position is IN the set of values we supply ‐Manager or Supervisor)


• SELECT staffNo, fName, lName, position FROM Staff s WHERE EXISTS (SELECT * FROM Branch b WHERE s.branchNo=b.branchNo AND city='London';

• EXISTS: Predicate is true if list is non‐empty (i.e. it exists); so in the above example it is true if only for use with


p ysubqueries.

Querying Multiple Tables

PropertyForRent

PropertyNo Street City Postcode Type Rooms Rent OwnerNo StaffNo BranchNo

PA14 16 Holhead Aberdeen AB7 5SU House 6 650 CO46 SA9 B007

PG16 5 Novar Dr Glasgow G12 9AX Flat 4 450 CO93 SG14 B003

PG21 18 Dale Rd Glasgow G12 House 5 600 CO87 SG37 B003

PG36 2 Manor Rd Glasgow G32 4QX Flat 3 375 CO93 SG37 B003

PG4 6 Lawrence St Glasgow G11 9QX Flat 3 350 CO40 B003

•How do we list all the properties that a given client has viewed?•Could start with an example - e.g. client CR56 ...


PL94 6 Argyll St London NW2 Flat 4 400 CO87 SL41 B005

ViewingClientNo PropertyNo ViewDate Comment

CR56 PA14 24-May-01 too small

CR56 PG36 28-Apr-01

CR56 PG4 26-May-01

CR62 PA14 14-May-01 no dining room

CR76 PG4 20-Apr-01 too remote

ClientClientNo Fname Lname TelNo PrefType MaxRent

CR56 Aline Stewart 0141-848-1825 Flat 350

CR62 Mary Tregear 01224-196720 Flat 600

CR74 Mike Ritchie 01475-392178 House 750

CR76 John Kay 0207-774-5632 Flat 425

36

Property Query ‐ First Attempt

• First attempt: List the property numbers viewed by client number 'CR56':

SELECT PropertyNoFROM ViewingWHERE ClientNo = 'CR56';

• But we'd like to see the client name & property details• So we'll need to access Client and PropertyForRent for

names etc


names etc...• To obtain info from >1 table: subqueries or joins; for result

table to contain columns from >1 table: join.• Recall subqueries: SELECT * FROM Staff WHERE branchNo =

(SELECT branchNo FROM Branch WHERE street = '163 Main St');

Property Query ‐ Second Version

SELECT DISTINCT Viewing.PropertyNo, Street, City, ViewDate

FROM Viewing, PropertyForRentWHERE ClientNo = 'CR56'AND Viewing.PropertyNo = PropertyForRent.PropertyNo; (matching

cols)


• We now have two table names in the FROM clause• Note use of “Table.ColumnName" to avoid ambiguity in

column names (i.e. both Viewing and PropertyForRenthave a PropertyNo column)

Property Query ‐ Third VersionSELECT DISTINCT Fname, Lname, Street, City, ViewDateFROM Viewing, PropertyForRent, ClientWHERE Viewing.ClientNo = 'CR56'AND Viewing.PropertyNo = PropertyForRent.PropertyNoAND Viewing.ClientNo = Client.ClientNo;


• The two “AND" clauses are called join criteria• Note for later: primary key= parent & foreign key=child: this is

parent/child relationship, or one‐to‐many (1:*), e.g. PropertyForRent/Viewing; more info on relational algebra can be found in !!.

Property Query ‐ Fourth Version

• Users shouldn't have to know about internal keys...SELECT DISTINCT Fname, Lname, Street, City, ViewDate

FROM Viewing, PropertyForRent, Client

WHERE Fname = 'Aline' AND Lname = 'Stewart'

AND Viewing.PropertyNo = PropertyForRent.PropertyNo;


AND Viewing.ClientNo = Client.ClientNo;

Using Table Aliases

• Table aliases can help reduce amount of typing• The following is identical to the previous query:

SELECT C.Fname, C.Lname, P.Street, P.City, V.ViewDate

FROM Viewing V, PropertyForRent P, Client CWHERE C.Fname = 'Aline' AND C.Lname = 'Stewart'


215

AND V.PropertyNo = P.PropertyNoAND V.ClientNo = C.ClientNo;

• Table aliases help reduce the risk of typing mistakes• But shouldn't the DBMS know how to match keys for us? Only if they appear in 1 table

Simple JoinsSELECT c.clientNo, fName, lName, propertyNo

FROM Client c, Viewing v

WHERE c.clientNo = v.clientNo; implicit join

SELECT c.clientNo, fName, lName, propertyNo

FROM Client c

JOIN Viewing v ON c.clientNo = v.clientNo; ‐> 2 clientNo cols


FROM Client JOIN Viewing USING clientNo; explicit join


216

g ; p j


FROM Client NATURAL JOIN Viewing; (only joins matched rows)

3 table query:

SELECT c.clientNo, c.fName, c.lName, p.propertyNo

FROM Client c, Viewing v, PropertyForRent p

WHERE c.clientNo = v.clientNo AND v.propertyNo = p.propertyNo;

• ORDER BY still works, just specify table.colName

• Specify table.colNo when colNo appears in >1 table; can also do this to be clearer

37

Cross Joins (Cartesian Products)

• Cartesian Product: a join with no WHERE clause, selects everything from both tables (most general join)

SELECT * FROMLeft, Right;

• mySQL allows:SELECT * FROM


217

Left CROSS JOIN Right;• Useful for:

– query optimisation– data mining

• Inner joins are type of cross join• Inner join (a type of cross join) only returns rows which

meet specified criteria, can be equijoins (a type of theta join which uses only =), or natural joins (a type of equijoin which selects rows w/ common values); Outer join returns matching & unmatching rows

Natural Joins

• Natural joins implement relationships in the Relational model• They are a type of equijoin which selects rows with common values

between tables • The DBMS will know which columns are key columns• The following queries are equivalent:

SELECT C.Fname, C.Lname, P.Street, P.City, V.ViewDateFROM Client C NATURAL JOIN


218

FROM Client C NATURAL JOIN(Viewing V NATURAL JOIN PropertyForRent P)WHERE C.Fname = 'Aline' AND C.Lname = 'Stewart';andSELECT C.Fname, C.Lname, P.Street, P.City, V.ViewDateFROM Viewing V, PropertyForRent P, Client CWHERE C.Fname = 'Aline' AND C.Lname = 'Stewart'AND V.PropertyNo = P.PropertyNoAND V.ClientNo = C.ClientNo;

• Most DBMSs support 4‐table joins, or more...

mySQL Syntax for Joins

• mySQL allows joins to be written in different ways:

• Natural joins:SELECT * FROM Left NATURAL JOIN Right;SELECT * FROM Left JOIN Right USING ColNam;

• If not joining on keys, give join condition explicitly:


219

SELECT * FROM Left JOIN Right

ON Left.ColNam = Right.ColNam;

• You can do implicit joins

• Which is best ? ‐Make up your own mind, but be aware with how they relate to each other

Theta Joins

• “Theta join" is a type of inner join (only returns rows which meet specified criteria) which have a more general WHERE predicate than equijoins (which only match on equality):

SELECT L.*, R.*, ...FROM Left L, Right RWHERE L.LeftCol Θ R.Rightcol;


220

• Θmay be one of =; ! =; <>; <; >; <=; >=• If Θ is =, its an equi join• If Θ is = and matches on key columns its a natural join• If all output columns are from one table, its a semi join

(equivalent to a subquery)

Example of a Theta Join

• For all clients, list the properties that each client can afford to rent:

SELECT C.ClientNo, P.PropertyNo

FROM Client C, PropertyForRent P

WHERE C MaxRent >= Prent;


221

WHERE C.MaxRent >= P.rent;

• The DBMS could implement theta joins by:

– First forming a cross join to give...

– An intermediate (Cartesian product) table..

– Then applying WHERE clause to find matching rows

– Notice that the relation is >= not =

Self‐Joins

• Sometimes it is useful to join a table to itself (must use aliases)

ALTER TABLE Staff ADD COLUMN BossNo CHAR(5);

SELECT S.Lname AS Person, B.Lname as Boss

FROM Staff S, Staff B


,

WHERE S.BossNo = B.StaffNo;

38

Outer Joins(Selecting unmatched rows)

• Inner join (a type of cross join) only returns rows which meet specified criteria, can be equijoins (a type of theta join which uses only =), or natural joins (a type of equijoin which selects rows w/ common values); Outer join returns matching & unmatching rows

• Example: List the branch offices and properties in the same city, along with any unmatched branches:

SELECT B.BrNo, P.PropNoFROM PropForRent P RIGHT JOIN Branch B ON B.City = P.City;


• NB. Not all DBMSs (e.g. Microsoft Access) support outer joins

Right Outer Joins & Full Outer Joins

• In a similar manner, can use RIGHT JOIN and FULL JOIN (meaning full outer join):

SELECT B.BrNo, P.PropNo

FROM Branch B FULL JOIN PropertyForRent P

ON B Cit PCit


ON B.City = P.City;

Types of Join

• Theta join ‐ inner join using a simple WHERE predicate

• Equi join ‐ a special case of theta join (= predicate)

• Natural join ‐ special case of equi join (match keys)

• Semi join ‐ theta join that outputs from just one table


225

• Self join ‐ joining a table to itself

• Outer join ‐may include unmatched rows; left/right/full

• Inner join – a join that only includes matched rows

• Cross join ‐ Cartesian products (no predicates); most general

Types of Join

• Explicit join uses the keyword JOIN,

• Implicit join does not use the keyword JOIN– specifies a cross‐join– WHERE clause may apply additional filter‐predicates– filter‐predicates function comparably to join‐predicates in the

explicit notation


226

explicit notation.

• Why do we need to distinguish so many different types of join ?

• Queries with different joins are often optimiseddifferently...

• Lots of online resources, e.g., http://www.w3schools.com/sql/, www.wikipedia.org, etc. The Web is your friend.


SQL 4:


227

Implementing Relationships Using Keys & Using Natural Joins

Dr. Stuart Kerrigan

Previously on CO1019

• Queries involving multiple tables

• Different types of join

– Natural Join uses keys specified in table

• Relationships

– 1‐* relationships

– 1‐1 relationships

– *‐* relationships


228

39


• SQL data types & related scalar functions• How to declare

– primary keys– foreign keys

i i d d l

229

– unique indexed columns• And how to ensure MySQL maintains the integrity constraints

• How integrity constraints can affect row operations

SQL's Integrity EnhancementFeatures (IEF)

• Real databases are often very ‘active’ with 100s of users simultaneously querying and updating the DB.

• So database integrity is important• IEFs allow the DB designer to specify & enforce:

– domain constraints

230

domain constraints– required data– entity integrity– referential integrity– enterprise constraints (business rules)

Creating Tables ‐ Data Definition

• CREATE TABLE is used to define relational tables

• Defines the data type for each column

• Also defines rules for how data is inserted and deletedCREATE TABLE Staff (StaffNo VARCHAR(5),Lname VARCHAR(20),

231

Salary FLOAT,HireDate DATE);

• VARCHAR, FLOAT, and DATE are examples of domains

• Also some rules are implied here– StaffNo is up to 5 characters long,

– Lname is 20 characters long

• Domains specify type & range of allowed data values

Built‐in Data Types (Domains) in MySQL

• SQL supports many data types (vendors often also have own dialects):– CHARACTER (CHAR), CHARACTER VARYING (VARCHAR)– NUMERIC, DECIMAL (DEC), INTEGER (INT), SMALLINT– FLOAT, REAL, DOUBLE PRECISION

232

– DATE, TIME, TIMESTAMP– BOOLEAN, BIT– BINARY LARGE OBJECT (BLOB), etc.

• Some types have an associated size . e.g. CHAR(5)

Required Data& More Domain Constraints

• NOT NULL means row can not contain nulls• Example:

CREATE TABLE Staff (StaffNo VARCHAR(5) NOT NULL,Lname VARCHAR(20) NOT NULL,Salary FLOAT CHECK (Salary BETWEEN 5050

and 20000),HireDate DATE);

• StaffNo & Lname are required ‐may not be NULL• Domain Constraints: specifies what’s ok in col/table• CHECK gives a domain constraint for Salary• Updates & insertions will fail if constraints not satisfied

Scalar Functions

• Scalar functions may be used to convert/manipulate data values (remember aggregates: MIN, MAX, etc.)

• Example:SELECT SUBSTRING(Lname, 1, 3),CONVERT(INTEGER Salary),EXTRACT(YEAR FROM HireDate)

234

FROM Staff;

• MySQL supports many scalar functions

ResultSMI 12075 1990

40

Entity Integrity ‐ Primary Keys• Reminder: the primary key of each row in a table must

be unique and non‐null.

• Example: The primary key of the Viewing table is composed of two attributes (composite key):

CREATE TABLE Viewing (ClientNo VARCHAR(5) NOT NULL,

235

PropertyNo VARCHAR(5) NOT NULL,PRIMARY KEY (ClientNo, PropertyNo))ENGINE=INNODB;

• The primary key of this table is a composite key

• SQL will reject operations that would violate primary key uniqueness

Entity Integrity ‐ Primary Keys• Primary key of the Guest table in a hotel database is

one attribute:‐CREATE TABLE Guest (GuestNumber INT NOT NULL,FirstName VARCHAR(15),LastName VARCHAR(15),PRIMARY KEY (GuestNumber)) ENGINE=INNODB;

• ENGINE=INNODB required to handle all keys.

• What about foreign keys?

• What about unique foreign keys for 1‐1 relationships

236

Referential Integrity ‐ Foreign Keys

• Foreign key links a child table to parent table. If non‐null, should match a row of parent table.

• SQL has keywords for this:CREATE TABLE Room(RoomName VARCHAR(20) NOT NULL,GuestNumber INT NOT NULL,

237

,FOREIGN KEY (GuestNumber) REFERENCES Guest(GuestNumber),PRIMARY KEY (RoomName)) ENGINE=INNODB;

• SQL will reject operations that would violate referential integrity

Populate TablesGuestGuestNumber (Primary Key)

First Name LastName

1 Bob Hope

2 Tim Gall


238

3 Anne Example

4 Gilmore Running

INSERT INTO Guest VALUES (1,'Bob','Hope'), (2,'Tom', 'Gall'), (3,'Anne','Example'), (4,'Gilmore','Running');

Populate Tables

Room GuestGuestNumber (Primary Key)

First Name LastName

1 Bob Hope

2 Tim Gall

3 Anne Example

4 Gilmore Running

RoomName(Primary Key)

GuestNumber(Foreign Key)

Oakley Room 1

SamhayneRoom

1

Wood Room 2

Stoat Room 3


239

Stoat Room 3

Eagle Room 4

INSERT INTO Guest VALUES (1,'Bob','Hope'), (2,'Tom', 'Gall'), (3,'Anne','Example'), (4,'Gilmore','Running');INSERT INTO Room VALUES ('Oakley Room',1), ('Samhayne Room',1),('Wood Room',2),('Stoat Room',3), ('Eagle Room',4);

Using a Natural Join

SELECT RoomName, FirstName, LastName

FROM Guest NATURAL JOIN Room;


240

Room Guest0..* 1..1

41

UNIQUE Values• UNIQUE ( cols )

• Example:CREATE TABLE Room(RoomName VARCHAR(20) NOT NULL,GuestNumber INT NOT NULL,UNIQUE (GuestNumber),FOREIGN KEY (G tN b ) REFERENCES G tFOREIGN KEY (GuestNumber) REFERENCES Guest(GuestNumber),PRIMARY KEY (RoomName)) ENGINE=INNODB;

• 1 guest must occupy 1 room – so no

• What happens if we remove NOT NULL on GuestNumber?

241

Repopulate TablesRoom Guest

GuestNumber (Primary Key)

First Name LastName

1 Bob Hope

2 Tim Gall



Oakley Room 1

SamhayneRoom

1


242

3 Anne Example

4 Gilmore Running

GuestNumber must be unique – this line would violate

integrity

Room

Wood Room 2

Stoat Room 3

Eagle Room 4



First Name LastName

1 Bob Hope

2 Tim Gall

3 Anne Example



Oakley Room 1

Wood Room 2

Stoat Room 3


243

4 Gilmore RunningEagle Room 4

INSERT INTO Guest VALUES (1,'Bob','Hope'), (2,'Tom','Gall'), (3,'Anne','Example'), (4,'Gilmore','Running');

INSERT INTO Room VALUES ('Oakley Room',1), ('Wood Room',2), ('Stoat Room',3), ('Eagle Room',4);

Relationships




244

Room Guest0..1 1..1

Relationships without Not Null

CREATE TABLE Room(RoomName VARCHAR(20) NOT NULL,GuestNumber INT, UNIQUE (GuestNumber), FOREIGN KEY (GuestNumber) REFERENCES Guest (GuestNumber), PRIMARY KEY (RoomName)) ENGINE=INNODB;


245

Room Guest

0..1 0...1



First Name LastName

1 Bob Hope

2 Tim Gall

3 Anne Example

4 Gilmore Running



Oakley Room 1

Wood Room 2

Stoat Room 3

Eagle Room 4


246

4 Gilmore RunningEagle Room 4

Haunted Room NULL

INSERT INTO Guest VALUES (1,'Bob','Hope'), (2,'Tom','Gall'), (3,'Anne','Example'), (4,'Gilmore','Running');

INSERT INTO Room VALUES ('Oakley Room',1), ('Wood Room',2), ('Stoat Room',3), ('Eagle Room',4) , ('Haunted Room‘,NULL);

42

Relationships




247

Room Guest1 0..1

Relationships

SELECT RoomName, FirstName, LastName FROM Room LEFT JOIN Guest ON Guest.GuestNumber=Room.GuestNumber;


248

Room Guest1 0..1

Relationships

SELECT RoomName, FirstName, LastName FROM Guest RIGHT JOIN Room ON Guest.GuestNumber=Room.GuestNumber;


249

Room Guest1 0..1

Relationships• MySQL only supports one‐to‐many or one‐to‐one relationships

• Implement many to many relationships via a third table

Room Guest0..* 0..*

is in MySQL a third table• Two one‐to‐many relationships A ‐> AB and B ‐> AB.

• The logical primary key for AB is formed from the two foreign keys


250

Room(A) 0..1 0..*

Guest(B)

0..* 0..1RoomAllocation

(AB)

represented by

Redesigning TablesCREATE TABLE Guest (GuestNumber INT NOT NULL,FirstName VARCHAR(15),LastName VARCHAR(15),PRIMARY KEY (GuestNumber)) ENGINE=INNODB;

CREATE TABLE Room(RoomName VARCHAR(20) NOT NULL,PRIMARY KEY (RoomName))ENGINE=INNODB;

CREATE TABLE RoomAllocation(RoomName VARCHAR(20) NOT NULL, GuestNumber INT NOT NULL, FOREIGN KEY (GuestNumber) REFERENCES Guest (GuestNumber), FOREIGN KEY (RoomName) REFERENCES Room (RoomName), PRIMARY KEY (GuestNumber, RoomName)) ENGINE=INNODB;


251

Room(A) 0..1 0..*

Guest(B)

0..* 0..1Room

Allocation

(AB)

Repopulate Tables

Room GuestNumber (Primary Key)

First Name

LastName

1 Bob Hope

2 Tanya Hope

3 Anne Example


Oakley Room

Stoat Room

Eagle Room

Guest

RoomName(Composite Primary Key and Foreign Key)

GuestNumber(Composite PrimaryKey and Foreign Key)

Oakley Room 1

Oakley Room 2

Stoat Room 3

RoomAllocation


252

INSERT INTO Guest VALUES (1,'Bob','Hope'),(2,'Tanya', 'Hope'),(3,'Anne','Example');INSERT INTO Room VALUES ('Oakley Room'),('Stoat Room'),('Eagle Room');INSERT INTO RoomAllocation VALUES ('Oakley Room',1),('Oakley Room',2),('Stoat Room',3),('Eagle Room',3);

Eagle Room 3

43

RelationshipsSELECT FirstName, LastName, Room.RoomName FROM Guest NATURAL JOIN (Room NATURAL JOIN RoomAllocation);


253

Room Guest0..* 0..*

Referential Integrityand Referential Actions

• Question: if a key attribute in the parent table is modified, what should happen in the child table ? ‐ SQL provides 4 alternative referential actions:

• ON UPDATE & ON DELETE specify referential actions which determines what happens when an attempt to UPDATE or DELETE a candidate key in a parent table which has matching rows in child table:

FOREIGN KEY (Key) REFERENCES Table [ON DELETE | UPDATE Action]– CASCADE ‐ apply changes to child rows (could trickle down)

254

CASCADE apply changes to child rows (could trickle down)– SET NULLDEFAULT ‐ set child keys to NULL– SET ‐ set child keys to DEFAULT value– NO ACTION ‐ reject the operation (default)

• Suppose a room’s name is changed. What is the most appropriate action?• Suppose a room is deleted. What is the most appropriate action?


CREATE TABLE RoomAllocation(RoomName VARCHAR(20) NOT NULL,GuestNumber INT NOT NULL,FOREIGN KEY (GuestNumber) REFERENCES Guest (GuestNumber) ON UPDATE CASCADE,FOREIGN KEY (RoomName) REFERENCES Room (RoomName) ON UPDATE CASCADE,PRIMARY KEY (GuestNumber, RoomName)) ENGINE=INNODB;

255

RoomRoomName(Primary Key)

Oakley Room

Stoat Room

Eagle Room



Oakley Room 1

Oakley Room 2

Stoat Room 3

Eagle Room 3

RoomAllocation


INSERT INTO Room VALUES ('Oakley Room'),('Stoat Room'),('Eagle Room');

INSERT INTO RoomAllocation VALUES ('Oakley Room',1),('Oakley Room',2),('Stoat Room',3),('Eagle Room',3);

UPDATE Room SET RoomName = 'Condor Room' WHERE

256

UPDATE Room SET RoomName = Condor Room WHERE RoomName = 'Oakley Room';


Oakley Room

Stoat Room

Eagle Room



Oakley Room 1

Oakley Room 2

Stoat Room 3

Eagle Room 3

RoomAllocation




UPDATE RoomAllocation SET RoomName = 'Condor

257

UPDATE RoomAllocation SET RoomName = Condor Room' WHERE RoomName = 'Oakley Room';


Condor Room

Stoat Room

Eagle Room



Oakley Room 1

Oakley Room 2

Stoat Room 3

Eagle Room 3

RoomAllocation




UPDATE RoomAllocation SET RoomName = 'Condor

258

UPDATE RoomAllocation SET RoomName = Condor Room' WHERE RoomName = 'Oakley Room';


Condor Room

Stoat Room

Eagle Room



Condor Room 1

Condor Room 2

Stoat Room 3

Eagle Room 3

RoomAllocation

44

Enterprise Constraints(Business Rules)

• Sometimes, real‐world business rules involve constraints that refer to more than one table. Its useful to define enterprise constraints just once.

• Example: A member of staff may manage no more than 100 properties:

259

than 100 properties:CREATE ASSERTION StaffNotOverLoadedCHECK (NOT EXISTS(SELECT StaffNo FROM PropertyForRentGROUP BY StaffNo HAVING COUNT (*) > 100));CREATE TABLE PropertyForRent ( ...CONSTRAINT StaffNotOverLoaded);

Database Schemas Evolve Over Time

• Ideally, a database is created once and then used for many years ... BUT

• The data model may be improved (integrity, performance) ...

N f b dd d i l

260

• New features may be added in new releases ...

• Enterprise rules may change ...

• Therefore, SQL provides many options for changing tables:

• See ALTER TABLE in the MySQL Documentation

Summary So Far...

• DBs are ‘active’ or ‘alive’ ‐ contents always changing

• The structure of a DB can also evolve over time...

• DB contents should always be consistent ‐ integrity

• ANSI SQL provides several Integrity Enhancement Features (IEFs)

261

(IEFs)

• IEF => domain constraints, entity/referential integrity, business rules...

• IEFs imply additional design choices for new DBs

• One DBMS can manage multiple DBs ‐ notion of schemas & privileges


SQL 5: Views and the Data Control Language


262

SQL 5: Views and the Data Control Language

Dr. Stuart Kerrigan

Previously on CO1019

• Data Definition Language– CREATE DATABASE, DROP DATABASE etc.

– CREATE TABLE, ALTER TABLE, DROPCREATE TABLE, ALTER TABLE, DROP TABLE

• Data Manipulation Language– SELECT, UPDATE, DELETE, INSERT

• What about Data Control Language?

263


• the principles of object (tables, etc.) ownership & privileges

• what virtual tables (views) are and why they are useful

h i d fi d & i i• how views are defined & some constraints on views

• how views can be implemented & some processing issues

• how views & privileges may be combined to provide access control

264

45

The Importance of Views & Privileges

• DBMSs are primarily used in organisations, and in large organisations, DBMSs are used by a range of staff:– directors, managers, analysts, engineers, personnel, secretarial, etc.

• Consequently, access to data in different tables may need to be controlled to:– provide access to authorised users

– restrict access to unauthorised users (security)…what could happen if a db was hacked?!

– enforce business rules or government regulations

• Views & privileges can help implement access control ...

265

SQL's Access Control Model

• Access Control in SQL is similar to multi‐user operating systems (e.g. Unix, Windows, ...)

• A user supplies an Authorisation Id and password to the DBMS

• The DBMS opens a session for the user• The DBMS runs SQL statements on behalf of the user

Th b th f bj t h t• The user becomes the owner of any objects he creates• By default, only the owner may access his objects• The owner may grant and revoke access privileges to other

users • This is discretionary access control• Mandatory access control: strictly ordered classification level

of db objects & users are given clearance levels (not supported by SQL)

266

Granting Privileges• Discretionary access based on authorization identifiers

(username&password), ownership (specified by auth.id.) & privileges (actions user can carry out on the given table, e.g., SELECT, etc.)

• GRANT { PrivilegeList | ALL PRIVILEGES } ON ObjectNameTO { AuthIdList | PUBLIC } [ WITH GRANT OPTION ]

• where (typically):– ObjectName is a table– PrivilegeList may be a combination of:

• SELECT, INSERT, UPDATE, DELETE (can specify column names)• REFERENCES (column names referenced by integrity constraints, e.g.,

check or foreign key constraints)• USAGE (use of domain definitions)• WITH GRANT OPTION means users in AuthIdList can pass on

privileges to others

267

Examples of UsingSQL Access Control

• Allow any member of staff (with an Auth ID) to access the Client table:

GRANT ALL PRIVILEGES ON Client TO PUBLIC

• Allow only personnel staff to hire staff or to change their salaries:

GRANT SELECT, INSERT, UPDATE (Salary) ON Staff TO personnel

• Privileges are revoked in a similar manner:REVOKE { PrivilegeList | ALL PRIVILEGES }ON ObjectNameFROM { AuthIdList | PUBLIC } [ RESTRICT | CASCADE ]Recall: CASCADE will delete all related objects which reference the table, and RESTRICT will reject the DROP if there are dependent objects

268

What are Views?

• A view is a virtual table, constructed from base tables• Why would we want to do this?• Only the definition of a view is stored permanently (as a

query)• A view is realised dynamically when it is first referenced

3 f i h i l i l d/j i d• 3 types of views: horizontal, vertical, grouped/joined• Views are manipulated like other DBMS objects:

CREATE VIEW ViewName ... (next slide)DROP VIEW ViewName;GRANT ALL PRIVILEGES ON ViewName TO PUBLIC;REVOKE ALL PRIVILEGES ON ViewName FROM PUBLIC;

269

Creating Views ‐ Horizontal Views

• A horizontal view restricts the rows that may be seen:CREATE VIEW Manager3Staff AS (subselect)

SELECT * FROM Staff WHERE BranchNo = 'B003'; (defining query)

• Then...SELECT * FROM Manager3Staff;So now branch manager can only see details of her own branch

Manager3Staff

StaffNo Fname Lname Position Sex Salary BranchNo

SG37 Ann Beech Assistant F 12000 B003

SG5 Susan Brand Manager F 24000 B003

270

46

Creating Views ‐ Vertical Views

• A vertical view restricts the columns that may be seen:CREATE VIEW Staff3 AS (subselect/defining query)SELECT StaffNo, Fname, Lname, Position FROMManager3Staff; notice the view here!

• Then...SELECT * FROM Staff3;

• So now the viewer can’t see the salary info of staff members (only the y ( ymanager sees this)…

Staff3

StaffNo Fname Lname PositionSG37 Ann Beech Assistant

SG5 Susan Brand Manager

271

General Syntax for Creating Views

• General syntax:CREATE VIEW ViewName [ (NewColNames) ] ASSubSelect;

• The SubSelect clause is called the defining query

• To create a view, a user must have SELECT privilege on the b blbase tables

• Once created, views often behave like ordinary base tables ...

• Views can be used in SELECT or JOIN clauses

• Views can be updated (with some restrictions)

• DROP VIEW ViewName [RESTRICT|CASCADE]

272

Grouped & Joined Views

• Views can be used to help simplify complex queries

• Example: create a view showing the number of properties managed by each member of staff and the branches they work at:

CREATE VIEW StaffProperties (StaffNo, BranchNo,Properties) ASSELECT s.StaffNo, s.BranchNo, COUNT (*)FROM St ff P t F R tFROM Staff s, PropertyForRent pWHERE s.StaffNo = p.StaffNoGROUP BY s.BranchNo, s.StaffNo; ‐‐GROUP BY stmt in subselect grouped view

‐‐Multiple tables in subselect joined view

‐‐Joined View simplifies querying; now we just query the view

• Can now query StaffProperties as if it’s a base tableSELECT * FROM StaffProperties;

273

How Are Views Implemented?

• Most DBMSs implement views using view resolution, which translates stored query into actual query on src tables specified in the view

• SQL re‐writes the view references back to the underlying base tables

• view materialisation: alternative implementation

• SQL populates a temporary table when the view is first referenced and keeps it up‐to‐date

• However, keeping the temporary table up‐to‐date can be difficult...

• View materialisation is an active area of DB research

274

How to Access Other Users' Objects

In SQL, the full name of a table has the form:server.schema.owner.tablee.g. achilles.mcscw3.sk223.student

If the System Administrator (user 'sa') owns all of the DreamHome tables and user 'sbrand' manages Branch 3DreamHome tables, and user sbrand manages Branch 3,

The sa might enter:USE Dreamhome;GRANT SELECT ON Manager3Staff TO sbrand;

Then, user sbrand could reference the view as:SELECT * FROM Dreamhome.sa.Manager3Staff;

Or equally:SELECT * FROM Dreamhome.Manager3Staff;

275

Restrictions on Views• With views, some queries are not permitted:–Queries that resolve to nested aggregates, e.g., SELECT COUNT(cnt) FROM StaffPropCnt; (cnt is based on an aggregated fn)

Q i th t i t i–Queries that give aggregates in a WHERE clause, e.g., SELECT * FROM StaffPropCnt WHERE cnt>2; (cnt derived from an aggregate fn)

–Grouped views can’t be joined with a base table or view

276

47

Restrictions on Views• Views can be updated provided:

– There are no aggregates in the columns to be updated and DISTINCT isn’t specified (can’t eliminate duplicate rows from query results)

– There are no GROUP BY or HAVING clauses because this info doesn’t say where it came from; in INSERT INTO StaffPropCnt VALUES(‘B003’,’SG5’,2) we don’t know which 2 properties SG5 manages (don’t know appropriate primary key values in PropertyForRent)

– The view contains only one source table (i.e., no joined views, Unions, Int’s or set diff. (EXCEPT)) with no nested SELECTs; also every elt in SELECT must appear only 1x, & can only be a col

– Can’t violate integrity constraints of base table either (e.g.: no NULLs where NULLS not allowed)

– Otherwise (i.e., if the row/col in view can be traced back to its source table), changes to view means changes to base tables (i.e., view can be updatable)

277

Updating ViewsAn Important Subtlety

SQL allows a view to be updated provided the changed rows in the base tables still satisfy all of the conditions of the defining query's WHERE clause.

For example:UPDATE Manager3Staff SET BranchNo = 'B005'WHERE StaffNo = 'SG37';

This would fail because the modified row (BranchNo = 'B005') would no longer be selected by the view definition (WHERE BranchNo = 'B003').)◦ WITH CHECK OPTION of CREATE VIEW stmt: View updates may not

allow rows to migrate out of the view ◦ WITH LOCAL CHECK OPTION means any updates on this or related obj

can’t cause rows to disappear from this view unless it also disappears from the other view

◦ WITH CASCADED CHECK OPTION (default) means any updates on this view & on related views can’t cause rows to disappear from this view

◦ Can exploit this behaviour to help enforce DB integrity◦ Put domain/business constraints into the view definition & only

update views

278

Summary of Views• Advantages:

– Views help provide granularity of access control– Views can help reduce complexity (simplify tables & (e.g.) multi‐table queries) and

improve access control, e.g., customization (same tables can be seen differently by

different users) & convenience (users see only what they need), improved security (views appropriate for user, restricts access to db), constancy (view shows part of base tables & if base cols not in view chg, no effect), currency (changes to base table accessed in view are immediately seen in view)

– Views can help maintain DB integrity (e.g. by doing updates via views, recall that if WITH CHECK OPTION is used, all updates must satisfy defining query’s WHERE clause)

• Disadvantages:• Disadvantages:– There are some restrictions on their use: some views can’t be updated. can’t do

aggregates on aggregates in SELECT clause or use an aggregate fn in WHERE clause; also grouped views can’t be joined with a base table/view, etc.

– Implementation: resolution method can cause a performance penalty (here defining query is run on base tables again each time; prob w/ frequent access)

– Structure restriction: downside of constancy (SELECT * FROM Foo only selects cols which were in Foo when View was created; view needs to be recreated for new cols in Foo to appear in View)

– Materialisation method can cause consistency problems (stores temp table on first view query, but hard to maintain currency if base tables updated)

279

SQL ‐ Overall Summary• SQL is a powerful relational DB query language

• SQL is declarative, not procedural (e.g. no variables)

• SQL is showing its age ... (e.g. quirky syntax, bolted‐on features)

• But despite being over 25 years old...

• SQL remains THE ‘world‐standard’ for DBMSsSQL remains THE world standard for DBMSs

• Make sure you understand SELECT, JOIN, UPDATE etc. and qualifications of these & can extract the info you want; make sure you can do everything we’ve done in the practicals at the least

280

Next…

The Internet (done)

HTML (done)

Relational Databases (done)

MySQL (done)

281

y Q ( )

PHP(combining HTML & MySQL)

Chapter 0

Introduction to Computers

and

©The McGraw-Hill Companies, Inc. Permission required for reproduction or di l

4th Ed Chapter 0 - 282

Programming Languages

48

A History of Computers• Charles Babbage is credited as the father of computer. Although never

actually built, he proposed the computing machines called Difference Engine

and Analytical Engine that possessed the core characteristics of today’s

computers.

• Ada Lovelace, who wrote demonstration programs for Analytical Engine, is credited as the first programmer.



• The first modern computer was built by Atanasoff of Iowa State University in the late 1930s.

• An electromechanical computer MARK I was built by Howard Aiken of Harvard.

• The first completely electronic computer ENIAC I was built by Mauchly and Eckert of the University of Pennsylvania.

Computer Architecture

CPU

OutputDevices

Commu-i ti

RAM



CPUnicationDevices

InputDevices

StorageDevices

Progress of CPU Speed



For more information on Intel CPUs, click Intel Museum or Quick Reference Chart.

Programming Languages

• Three levels of programming languages:

– Machine Languages– Machine language instructions are binary coded and very low



Machine language instructions are binary coded and very low level.

– Assembly Languages– Assembly language allows symbolic programming. Requires an assembler to translate assembly programs into machine programs.

– High‐level Languages– High‐level language provides a very high conceptual model of computing. Requires a compiler to translate high‐level pograms into assembly programs.

Java

• Java is a high‐level object‐oriented language developed by Sun Microsystems.

• Java’s clean design and wide availability make it an ideal language for teaching the



it an ideal language for teaching the fundamentals of computer programming.

Chapter 1

Introduction to Object‐Oriented Programming and Software

Development

. 4th Ed Chapter 1 - 288

Animated Version

49

Objectives

After you have read and studied this chapter, you should be able to

• Name the basic components of object‐oriented programming

• Differentiate classes and objects.

• Differentiate class and instance methods• Differentiate class and instance methods.

• Differentiate class and instance data values.

• Draw program diagrams using icons for classes and objects

• Describe significance of inheritance in object‐oriented programs

• Name and explain the stages of the software lifecycle


Classes and Objects

• Object‐oriented programs use objects.

• An object is a thing, both tangible and intangible. Account, Vehicle, Employee, etc.

T t bj t i id th t• To create an object inside the computer program, we must provide a definition for objects—how they behave and what kinds of information they maintain —called a class.

• An object is called an instance of a class.


Graphical Representation of a Class

<Class Name> We use a rectangle to represent a class with its name appearing inside the rectangle.


The notation we used here is based on the industry standard notation called UML, which stands for Unified Modeling Language.

Example: Account Motorcycle

Graphical Representation of an Object

<Object Name>

We use a rectangle to represent an object and place the underlined name of the object inside the rectangle.


Example:

SV198This is an object named SV198.

An Object with the Class Name

<Object Name> : <Class Name>This notation indicates the class which the object is an instance.


This tells an object SV198 is an instance of the BankAccount class.

Example:

SV198 : BankAccount

Messages and Methods• To instruct a class or an object to perform a task, we send a

message to it.

• You can send a message only to the classes and objects that understand the message you sent to them.

• A class or an object must possess a matching method to be able to handle the received messageable to handle the received message.

• A method defined for a class is called a class method, and a method defined for an object is called an instance method.

• A value we pass to an object when sending a message is called an argument of the message.


50

Sending a Message

Message deposit with the argument 250.00 is sent to a BankAccount object SV198.


deposit 250.00SV198 : BankAccount

Sending a Message and Getting an Answer

getCurrentBalance()

Ask for the current balance of this particular account.


current balance

SV198 : BankAccount

The current balance of SV198 is returned.

Calling a Class Method

MobileRobot

Ask for the maximum possible speed for all MobileRobot objects is returned.


maximum speed

MobileRobot

getMaximumSpeed()

Class and Instance Data Values

• An object is comprised of data values and methods.

• An instance data value is used to maintain information specific to individual instances. For example, each BankAccount object maintains its balance.

• A class data value is used to maintain information shared by• A class data value is used to maintain information shared by all instances or aggregate information about the instances.

• For example, minimum balance is the information shared by all Account objects, whereas the average balance of all BankAccount objects is an aggregate information.


Sample Instance Data Value

SV098 : BankAccount SV211 : BankAccountSV129 : BankAccount

current balance current balance current balance

908.55 1304.98 354.00


All three BankAccountobjects possess the same instance data value current balance.

The actual dollar amounts are, of course, different.

Sample Class Data ValueBankAccount

minimum balance

100.00

There is one copy of minimum balance for the whole class and shared by all instances.

This line is an


SV098 : BankAccount SV211 : BankAccountSV129 : BankAccount

current balance current balance current balance

908.55 1304.98 354.00

This line is an instance-ofrelationship.

51

Object Icon with Class Data Value

When the class icon is not shown, we include

SV129 : BankAccount

minimum balance

100.00


the class data value in the object icon itself.current balance

908.55

Inheritance

• Inheritance is a mechanism in OOP to design two or more entities that are different but share many common features.

– Features common to all classes are defined in the– Features common to all classes are defined in the superclass.

– The classes that inherit common features from the superclass are called subclasses.

• We also call the superclass an ancestor and the subclass a descendant.


A Sample Inheritance

• Here are the superclass Account and its subclasses Savings and Checking.

Account


Checking Savings

Inheritance Hierarchy

• An example of inheritance hierarchy among different types of students.

Student


Graduate Undergrad

LawMasters Doctoral Commuting Resident

Software Engineering

• Much like building a skyscraper, we need a disciplined approach in developing complex software applications.

• Software engineering is the application of a systematic and disciplined approach to the development, testing, and maintenance of a program.

• In this class, we will learn how to apply sound software engineering principles when we develop sample programs.


Software Life Cycle

• The sequence of stages from conception to operation of a program is called software life cycle.

• Five stages are

– Analysis

– Design

– Coding

– Testing

– Operation and Maintenance


52

Chapter 2

Getting Started with Java


Objectives


• Identify the basic components of Java programs

• Write simple Java programs

• Describe the difference between object declaration and creation

• Describe the process of creating and running Java programs

• Use the Date, SimpleDateFormat, String, and JOptionPane standard classes

• Develop Java programs, using the incremental development approach


The First Java Program

• The fundamental OOP concept illustrated by the program:

An object‐oriented program uses objects.j

• This program displays a window on the screen.

• The size of the window is set to 300 pixels wide and 200 pixels high. Its title is set to My First Java Program.


Program Ch2Sample1

import javax.swing.*;class Ch2Sample1 {

public static void main(String[ ] args) {

JFrame myWindow;

myWindow = new JFrame( );

Declare a name

Create an object


myWindow new JFrame( );

myWindow.setSize(300, 200);

myWindow.setTitle("My First Java Program");

myWindow.setVisible(true);}

}

j

Use an object

Program Diagram for Ch2Sample1

myWindow : JFrame

Ch2Sample1

setTitle("My First Java Program")


myWindow : JFrame

Dependency Relationship

myWindow : JFrame

Ch2Sample1


Instead of drawing all messages, we summarize it by showingonly the dependency relationship. The diagram shows that Ch2Sample1 "depends" on the service provided by myWindow.

53

Object Declaration

JFrame myWindow;

Object NameOne object is declared here.

Class NameThis class must be defined before this declaration can be stated.


MoreExamples

Account personal;Student jan, jim, jon;Vehicle car1, car2;

Object Creation

myWindow = new JFrame ( ) ;

Object NameName of the object we are creating here.

Class NameAn instance of this class is created.

ArgumentNo arguments are used here.


MoreExamples

myCust = new Customer( );jon = new Student("John Java");car1 = new Vehicle( );

Declaration vs. Creation

Customer myCust;

myCust = new Customer( );

Customer myCust;


1

2


1. The identifier myCust is declared and space is allocated in memory.

2. A Customer object is created and the identifier myCust is set to refer to it.

myCust

1

: Customer2

State‐of‐Memory vs. Program

myCust

myCust : Customer


: Customer

State-of-MemoryNotation

Program DiagramNotation

Name vs. Objects

Customer myCust;



Customer myCust;




myCust

: Customer : CustomerCreated with the first new.

Created with the second new. Reference to the first Customer object is lost.

Sending a Message

myWindow . setVisible ( true ) ;

Object NameName of the object to which we are sending a message.

Method NameThe name of the message we are sending.

ArgumentThe argument we are passing with the message.


y ( )

MoreExamples

account.deposit( 200.0 );student.setName("john");car1.startEngine( );

54

Execution Flow

JFrame myWindow;



myWindow

State-of-Memory Diagram

: JFrame

Program Code



myWindow.setVisible(true);

width

height

title

visible

200

My First Java …

300

true

The diagram shows only four of the many data members of a JFrame object.

Program Components

• A Java program is composed of

– comments,

– import statements, and

– class declarations.


Program Component: Comment/*

Chapter 2 Sample Program: Displaying a Window

File: Ch2Sample2.java*/

import javax.swing.*;

class Ch2Sample1 {



JFrame myWindow;





}

Comment

Matching Comment Markers/* This is a comment on one line */

/*

Comment number 1

*/

/*

Comment number 2

*/


/

/*

/*

/*

This is a comment

*/

*/

Error: No matching beginning marker.

These are part of the comment.

Three Types of Comments/*

This is a comment with

three lines of

text.

*/

Multiline Comment


Single line Comments

// This is a comment

// This is another comment

// This is a third comment

/**

* This class provides basic clock functions. In addition

* to reading the current time and today’s date, you can

* use this class for stopwatch functions.

*/

javadoc Comments

Import Statement/*




class Ch2Sample1 {public static void main(String[ ] args) {

Import Statement


JFrame myWindow;





}

55

Import Statement Syntax and Semantics

<package name> . <class name> ;

Class NameThe name of the class we want to import. Use asterisks to import all classes.

Package NameName of the package that contains the classes we want to use.


e.g. dorm . Resident;

MoreExamples

import javax.swing.JFrame;import java.util.*;import com.drcaffeine.simplegui.*;

Class Declaration/*




class Ch2Sample1 {public static void main(String[ ] args) {

Class Declaration


JFrame myWindow;





}

Method Declaration/* Chapter 2 Sample Program: Displaying a Window

File: Ch2Sample2.java */


class Ch2Sample1 {


JFrame myWindow;

Method Declaration






}

Method Declaration Elements

public static void main( String[ ] args ){

JFrame myWindow; Method Body

Modifier Modifier Return Type Method Name Parameter


y





}

y

Template for Simple Java Programs/*




class Ch2Sample1 {


Import Statements

Class Name

Comment


JFrame myWindow;





}}

Class Name

Method Body

Why Use Standard Classes

• Don’t reinvent the wheel. When there are existing objects that satisfy our needs, use them.

• Learning how to use standard Java classes is the first step toward mastering OOP. Before we can learn how to define our own classes we need tolearn how to define our own classes, we need to learn how to use existing classes

• We will introduce four standard classes here: – JOptionPane – String– Date– SimpleDateFormat.


56

JOptionPane

• Using showMessageDialog of the JOptionPaneclass is a simple way to display a result of a computation to the user.

JO ti P h M Di l ( ll


JOptionPane.showMessageDialog(null, "I Love Java");

This dialog will appear at the center of the screen.

Displaying Multiple Lines of Text

• We can display multiple lines of text by separating lines with a new line marker \n.JOptionPane.showMessageDialog(null,

"one\ntwo\nthree");


String• The textual values passed to the showMessageDialog method are instances of the String class.

• A sequence of characters separated by double quotes is a String constant.double quotes is a String constant.

• There are close to 50 methods defined in the String class. We will introduce three of them here: substring, length, and indexOf.

• We will also introduce a string operation called concatenation.


String is an Object

1. The identifier name is

1

2

name

String name;

name = new String("Jon Java");

String name;

name = new String("Jon Java");


declared and space is allocated in memory.

2. A String object is created and the identifier name is set to refer to it.

name

1

2: String

Jon Java

String Indexing


The position, or index, of the first character is 0.

Definition: substring• Assume str is a String object and properly initialized to a string.

• str.substring( i, j ) will return a new string by extracting characters of str from position i to j‐1 where 0 i length of str, 0 j length of str and i jof str, and i j.

• If str is "programming" , then str.substring(3, 7) will create a new string whose value is "gram" because g is at position 3 and m is at position 6.

• The original string str remains unchanged.


57

Examples: substring

String text = "Espresso";

text.substring(6,8) "so"


text.substring(0,8)

text.substring(1,5)

text.substring(3,3)

text.substring(4,2)

"Espresso"

"spre"

error

""

Definition: length• Assume str is a String object and properly initialized to a string.

• str.length( ) will return the number of characters in str.

• If str is "programming" , then str.length( ) will return 11 because there are 11 characters in it.

• The original string str remains unchanged.


Examples: lengthString str1, str2, str3, str4;str1 = "Hello" ;str2 = "Java" ;str3 = "" ; //empty stringstr4 = " " ; //one space


str1.length( )

str2.length( )

str3.length( )

str4.length( )

5

4

1

0

Definition: indexOf• Assume str and substr are String objects and properly initialized.

• str.indexOf( substr ) will return the first position substr occurs in str.

• If str is "programming" and substr is "gram" , h d f( b ) llthen str.indexOf(substr ) will return 3 because the position of the first character of substr in str is 3.

• If substr does not occur in str, then –1 is returned.

• The search is case‐sensitive.


Examples: indexOfString str;str = "I Love Java and Java loves me.";

3 7 21


str.indexOf( "J" )

str2.indexOf( "love" )

str3.indexOf( "ove" )

str4.indexOf( "Me" )

7

21

-1

3

Definition: concatenation• Assume str1 and str2 are String objects and properly initialized.

• str1 + str2 will return a new string that is a concatenation of two strings.

• If str1 is "pro" and str2 is "gram" , then str1 + str2 will return "program".

• Notice that this is an operator and not a method of the String class.

• The strings str1 and str2 remains the same.


58

Examples: concatenation

String str1, str2;str1 = "Jon" ;str2 = "Java" ;

"J J "


str1 + str2

str1 + " " + str2

str2 + ", " + str1

"Are you " + str1 + "?"

"JonJava"

"Jon Java"

"Java, Jon"

"Are you Jon?"

Date• The Date class from the java.util package is used to represent a date.

• When a Date object is created, it is set to today (the current date set in the computer)

• The class has toString method that converts the ginternal format to a string.


Date today;today = new Date( );today.toString( );

"Fri Oct 31 10:05:18 PST 2003"

SimpleDateFormat

• The SimpleDateFormat class allows the Dateinformation to be displayed with various format.

• Table 2.1 page 68 shows the formatting options.

Date today new Date( )


Date today = new Date( );SimpleDateFormat sdf1, sdf2;sdf1 = new SimpleDateFormat("MM/dd/yy");sdf2 = new SimpleDateFormat("MMMM dd,yyyy");

sdf1.format(today);

sdf2.format(today);

"10/31/03"

"October 31, 2003"

JOptionPane for Input

• Using showInputDialog of the JOptionPaneclass is a simple way to input a string.

String name;name = JOptionPane.showInputDialog


p p g(null, "What is your name?");

This dialog will appear at the center of the screen ready to accept an input.

Chapter 3

Numerical Data


Animated Version

ObjectivesAfter you have read and studied this chapter, you should be able to

• Select proper types for numerical data.• Write arithmetic expressions in Java.• Evaluate arithmetic expressions using the precedence rules.• Describe how the memory allocation works for objects and primitive data valuesprimitive data values.

• Write mathematical expressions, using methods in the Math class.

• Use the GregorianCalendar class in manipulating date information such as year, month, and day.

• Use the DecimalFormat class to format numerical data• Convert input string values to numerical data• Perform input and output by using System.in and System.out


59

Manipulating Numbers

• In Java, to add two numbers x and y, we write

x + y

• But before the actual addition of the two b t k l t d l th inumbers takes place, we must declare their

data type. If x and y are integers, we write

int x, y;

orint x;int y;


Variables

• When the declaration is made, memory space is allocated to store the values of x and y.

• x and y are called variables. A variable has three properties:three properties:

– A memory location to store the value,

– The type of data stored in the memory location, and

– The name used to refer to the memory location.

• Sample variable declarations:

int x;int v, w, y;


Numerical Data Types

• Six numerical datatypes: byte, short, int, long, float & double.

• Sample variable declarations:int i, j, k; float numberOne, numberTwo; , ;long bigInteger;double bigNumber;

• At the time a variable is declared, it also can beinitialized. For example, we may initialize the integervariables count and height to 10 and 34 as

int count = 10, height = 34;


Data Type Precisions

The six data types differ in the precision of values they can store in memory.


h t

int

long

float

double

byte

short

Assignment Statements

• We assign a value to a variable using an assignment statements.

• The syntax is

<variable> = <expression> ;

• Examples:

sum = firstNumber + secondNumber;avg = (one + two + three) / 3.0;


60

Arithmetic Operators

• The following table summarizes the arithmetic operators available in Java.


This is an integer division where the fractional part is truncated.

Arithmetic Expression

• How does the expressionx + 3 * y

get evaluated? Answer: x is added to 3*y.

• We determine the order of evaluation byWe determine the order of evaluation by following the precedence rules.

• A higher precedence operator is evaluated before the lower one. If two operators are the same precedence, then they are evaluated left to right for most operators.


Precedence Rules


Type Casting

• If x is a float and y is an int, what will be the data type of the following expression?

x * y

The answer is float.

Th b i i ll d i d i• The above expression is called a mixed expression.

• The data types of the operands in mixed expressions are converted based on the promotion rules. The promotion rules ensure that the data type of the expression will be the same as the data type of an operand whose type has the highest precision.


Explicit Type Casting

• Instead of relying on the promotion rules, we can make an explicit type cast by prefixing the operand with the data type using the following syntax:following syntax:( <data type> ) <expression>

• Example (float) y / 3

(int) (x / y * 3.0)


Type case y to float and then divide it by 3.

Type cast the result of the expression x / y * 3.0 to int.

Implicit Type Casting• Consider the following expression:

double x = 3 + 5;

• The result of 3 + 5 is of type int. However, since the variable x is double, the value 8 (type int) is promoted to 8.0 (type double) ( yp ) p ( yp )before being assigned to x.

• Notice that it is a promotion. Demotion is not allowed.

int x = 3.5;


A higher precision value cannot be assigned to a lower precision variable.

61

Constants• We can change the value of a variable. If we want the value to remain the same, we use a constant.

final double PI = 3 14159;final double PI = 3.14159;final int MONTH_IN_YEAR = 12;final short FARADAY_CONSTANT = 23060;


These are constants, also called named constant.

The reserved word final is used to declare constants.

These are called literal constant.

Primitive vs. Reference

• Numerical data are called primitive data types.

• Objects are called reference data types, because the contents are addresses that refer to memory locations where the objects areto memory locations where the objects are actually stored.


Primitive Data Declaration and Assignments

A

int firstNumber, secondNumber;firstNumber = 234;secondNumber = 87;

firstNumber

A. Variables are allocated in memory.

234


Code State of Memory

int firstNumber, secondNumber;firstNumber = 234;secondNumber = 87;

int firstNumber, secondNumber;

BfirstNumber = 234;secondNumber = 87;

secondNumber

B. Values are assigned to variables.

87

Assigning Numerical Data

int number;number = 237;number = 35; number

A. The variable is allocated in

23735



is allocated in memory.

B. The value 237is assigned to number.

int number;

number = 237;

number = 35;

Aint number;

Bnumber = 237;

Cnumber = 35;

C. The value 35overwrites the

previous value 237.

Assigning Objects

Customer customer;customer = new Customer( );customer = new Customer( );

customer

A The variable is

A

B

Customer Customer



A. The variable is allocated in memory.

Customer customer;

customer = new Customer( );


Customer customer;B


C

customer = new Customer( );B. The reference to the

new object is assigned to customer.

C. The reference to another object overwrites the reference in customer.

Having Two References to a Single Object

Customer clemens, twain;clemens = new Customer( );twain = clemens;

A

B A Variables are

clemens

twain

Customer



Customer clemens, twain,

clemens = new Customer( );

twain = clemens;

Customer clemens, twain; Bclemens = new Customer( );

C

twain = clemens;

A. Variables are allocated in memory.

B. The reference to the new object is assigned to clemens.

C. The reference in clemens is assigned to customer.

62

Type Mismatch

• Suppose we want to input an age. Will this work?

int age;


age = JOptionPane.showInputDialog(null, "Enter your age");

• No. String value cannot be assigned directly to an int variable.

Type Conversion

• Wrapper classes are used to perform necessary type conversions, such as converting a String object to a numerical value.

int age;


gString inputStr;

inputStr = JOptionPane.showInputDialog(

null, "Enter your age");

age = Integer.parseInt(inputStr);

Other Conversion Methods


Sample Code Fragment

//code fragment to input radius and output//area and circumferencedouble radius, area, circumference;

String radiusStr = JOptionPane.showInputDialog(null, "Enter radius: " );

radius = Double.parseDouble(radiusStr);


p ( );

//compute area and circumferencearea = PI * radius * radius;circumference = 2.0 * PI * radius;

JOptionPane.showMessageDialog(null, "Given Radius: " + radius + "\n" + "Area: " + area + "\n" + "Circumference: " + circumference);

Overloaded Operator +

• The plus operator + can mean two different operations, depending on the context.

• <val1> + <val2> is an addition if both are numbers. If either one of them is a String, the it is a concatenation.

• Evaluation goes from left to right.g g


output = "test" + 1 + 2; output = 1 + 2 + "test";

The DecimalFormat Class

• Use a DecimalFormat object to format the numerical output.

double num = 123.45789345;

DecimalFormat df = new DecimalFormat("0.000");// h d i l l


//three decimal places

System.out.print(num);

System.out.print(df.format(num));

123.45789345

123.458

63

Standard Output

• The showMessageDialogmethod is intended for displaying short one‐line messages, not for a general‐purpose output mechanism.

• Using System.out, we can output multiple lines of text to the standard output window.


Standard Output Window

• A sample standard output window for displaying multiple lines of text.


• The exact style of standard output window depends on the Java tool you use.

The print Method

• We use the printmethod to output a value to the standard output window.

• The printmethod will continue printing from the end of the currently displayed output.

• Example• Example System.out.print( "Hello, Dr. Caffeine." );


The println Method

• We use println instead of print to skip a line.

int x = 123, y = x + x;System.out.println( "Hello, Dr. Caffeine." );System.out.print( " x = " );System.out.println( x );System.out.print( " x + x = " );


System.out.print( x + x );System.out.println( y );System.out.println( " THE END" );

Standard Input

• The technique of using System.in to input data is called standard input.

• We can only input a single byte using System.in directly.

• To input primitive data values, we use the p p ,Scanner class (from Java 5.0).


Scanner scanner = new Scanner(System.in);int num = scanner.nextInt();

Common Scanner Methods:

Method Example

nextByte( ) byte b = scanner.nextByte( );

nextDouble( ) double d = scanner.nextDouble( );

nextFloat( ) float f = scanner.nextFloat( );

nextInt( ) int i = scanner.nextInt( );

nextLong( ) long l = scanner.nextLong( );

nextShort( ) short s = scanner.nextShort( );

next() String str = scanner.next();


64

The Math class

• The Math class in the java.lang package contains class methods for commonly used mathematical functions.

double num, x, y;x = ;


x …;y = …;num = Math.sqrt(Math.max(x, y) + 12.4);

• Table 3.6 in the textbook contains a list of class methods defined in the Math class.

Some Math Class MethodsMethod Description

exp(a) Natural number e raised to the power of a.

log(a) Natural logarithm (base e) of a.

floor(a) The largest whole number less than or equal to a.

max(a b) The larger of a and b.


max(a,b)

pow(a,b) The number a raised to the power of b.

sqrt(a) The square root of a.

sin(a) The sine of a. (Note: all trigonometric functions are computed in radians)

Table 3.8 page 113 in the textbook contains a list of class methods defined in the Math class.

Chapter 4

Defining Your Own Classes

Part 1


Animated Version


• Define a class with multiple methods and data members

• Differentiate the local and instance variablesDifferentiate the local and instance variables

• Define and use value‐returning methods

• Distinguish private and public methods

• Distinguish private and public data members

• Pass both primitive data and objects to a method

Why Programmer‐Defined Classes

• Using just the String, GregorianCalendar, JFrameand other standard classes will not meet all of our needs. We need to be able to define our own classes customized for our applications. pp

• Learning how to define our own classes is the first step toward mastering the skills necessary in building large programs.

• Classes we define ourselves are called programmer‐defined classes.


First Example: Using the Bicycle Classclass BicycleRegistration {

public static void main(String[] args) {

Bicycle bike1, bike2;

String owner1, owner2;

bike1 = new Bicycle( ); //Create and assign values to bike1

bike1.setOwnerName("Adam Smith");


bike2 = new Bicycle( ); //Create and assign values to bike2

bike2.setOwnerName("Ben Jones");

owner1 = bike1.getOwnerName( ); //Output the information

owner2 = bike2.getOwnerName( );

System.out.println(owner1 + " owns a bicycle.");

System.out.println(owner2 + " also owns a bicycle.");

}

}

65

The Definition of the Bicycle Classclass Bicycle {

// Data Member private String ownerName;//Constructor: Initialzes the data memberpublic Bicycle( ) {

ownerName = "Unknown";}


//Returns the name of this bicycle's ownerpublic String getOwnerName( ) {

return ownerName;}

//Assigns the name of this bicycle's ownerpublic void setOwnerName(String name) {

ownerName = name;}

}

Multiple Instances• Once the Bicycle class is defined, we can create multiple instances.

Bicycle bike1, bike2;

bike1 bike2

: Bicycle: Bicyclebik 1 i l ( )


y

ownerName

y

ownerName

"Adam Smith" "Ben Jones"

bike1 = new Bicycle( );

bike1.setOwnerName("Adam Smith");

bike2 = new Bicycle( );

bike2.setOwnerName("Ben Jones");

Sample Code

The Program Structure and Source Files

BicycleRegistration Bicycle

There are two source files


There are two source files. Each class definition is stored in a separate file.

BicycleRegistration.java Bicycle.java

To run the program: 1. javac Bicycle.java (compile)2. javac BicycleRegistration.java (compile)3. java BicycleRegistration (run)

Class Diagram for Bicycle

Bicycle

Bicycle( )


Method ListingWe list the name and the data type of an argument passed to the method.setOwnerName(String)

Bicycle( )

getOwnerName( )

Template for Class Definition

class {

Import Statements

Class Comment

Class Name


}

Data Members

Methods(incl. Constructor)

Data Member Declaration

<modifiers> <data type> <name> ;

Modifiers Data Type Name


private String ownerName ;

Modifiers Data Type Name

Note: There’s only one modifier in this example.

66

Method Declaration<modifier> <return type> <method name> ( <parameters> ){

<statements>

}

Modifier Return Type Method Name Parameter


public void setOwnerName ( String name ) {

ownerName = name;

}

Statements

yp

Constructor• A constructor is a special method that is executed when a new instance of the

class is created.

public <class name> ( <parameters> ){<statements>

}


public Bicycle ( ) {

ownerName = "Unassigned";

}Statements

Modifier Class Name Parameter

Second Example: Using Bicycle and Account

class SecondMain {

//This sample program uses both the Bicycle and Account classes

public static void main(String[] args) {

Bicycle bike;Account myAcct;

String myName = "Jon Java";

bike = new Bicycle( ); bike setOwnerName(myName);


bike.setOwnerName(myName);

myAcct = new Account( );myAcct.setOwnerName(myName);myAcct.setInitialBalance(250.00);

myAcct.add(25.00);myAcct.deduct(50);

//Output some information System.out.println(bike.getOwnerName() + " owns a bicycle and"); System.out.println("has $ " + myAcct.getCurrentBalance() +

" left in the bank");

}}

The Account Classclass Account {

private String ownerName;

private double balance;

public Account( ) {ownerName = "Unassigned";balance = 0.0;

}

public void add(double amt) {balance = balance + amt;

}

public void setInitialBalance(double bal) {

balance = bal;}

public void setOwnerName(String name) {

ownerName = name;}

}


public void deduct(double amt) {balance = balance - amt;

}

public double getCurrentBalance( ) {return balance;

}

public String getOwnerName( ) {

return ownerName;}

Page 1 Page 2

The Program Structure for SecondMain

SecondMain

Bicycle

Account


SecondMain.java Bicycle.java

To run the program: 1. javac Bicycle.java (compile)2. javac Account.java (compile)2. javac SecondMain.java (compile)3. java SecondMain (run)

Account.java

Note: You only need to compile the class once. Recompile only when you made changes in the code.

Arguments and Parametersclass Account {

. . .

public void add(double amt) {

balance = balance + amt;}

. . .}

class Sample {

public static void main(String[] arg) {

Account myAcct = new Account();. . .

myAcct.add(400);. . .

}

. . .}

argument

parameter

• An argument is a value we pass to a method


• A parameter is a placeholder in the called method to hold the value of the passed argument.

67

Matching Arguments and Parameters

• The number or arguments and the parameters must be the same

Demo myInst = new Demo( );

int i = 5; int k = 14;

myInst.compute(i, k, 20);3 arguments

• Arguments and parameters are Passing Side


class Demo {

public void compute(int i, int j, double x) {. . .

}} 3 parameters

• The matched pair must be assignment-compatible (e.g. you cannot pass a double argument to a int parameter)

ppaired left to right

Receiving Side

Memory Allocation

• Separate memory space is allocated for the receiving method.

i 5

k 14

20

i

j

x

5

14

20.0• Values of


Passing Side Receiving Side

Values of arguments are passed into memory allocated for parameters.Literal constant

has no name

Passing Objects to a Method

• As we can pass int and double values, we can also pass an object to a method.

• When we pass an object, we are actually passing the reference (name) of an objectpassing the reference (name) of an object

– it means a duplicate of an object is NOT created in the called method


Passing a Student Object

class LibraryCard {private Student owner;bli id tO (St d t t) {

LibraryCard card2;

card2 = new LibraryCard();

card2.setOwner(student);

Passing Side

student

card2

st1

1

2


public void setOwner(Student st) {

owner = st;}

}

Receiving Side

: LibraryCard

owner

borrowCnt

0

: Student

name

"Jon Java"

email

"[email protected]"Argument is passed1

2

2 Value is assigned to thedata member State of Memory

Sharing an Object

• We pass the same Student object to card1 and card2


• Since we are actually passing a reference to the same object, it results in owner of two LibraryCard objects pointing to the same Student object

Information Hiding and Visibility Modifiers

• The modifiers public and private designate the accessibility of data members and methods.

• If a class component (data member or method) is declared private, client classes cannot access it.declared private, client classes cannot access it.

• If a class component is declared public, client classes can access it.

• Internal details of a class are declared private and hidden from the clients. This is information hiding.


68

Accessibility Example

class Service {public int memberOne;private int memberTwo;

public void doOne() {

…

…

Service obj = new Service();

obj.memberOne = 10;


}private void doTwo() {

…

}

}

obj.memberTwo = 20;

obj.doOne();

obj.doTwo();

…

Client Service

Data Members Should Be private

• Data members are the implementation details of the class, so they should be invisible to the clients. Declare them private .

• Exception: Constants can (should) be declaredException: Constants can (should) be declared public if they are meant to be used directly by the outside methods.


Guideline for Visibility Modifiers

• Guidelines in determining the visibility of data members and methods: – Declare the class and instance variables private.

– Declare the class and instance methods private if pthey are used only by the other methods in the same class.

– Declare the class constants public if you want to make their values directly readable by the client programs. If the class constants are used for internal purposes only, then declare them private.


Diagram Notation for Visibility


public – plus symbol (+)private – minus symbol (-)

Class Constants• In Chapter 3, we introduced the use of constants.

• We illustrate the use of constants in programmer‐defined service classes here.

• Remember, the use of constants– provides a meaningful description of what the valuesprovides a meaningful description of what the values stand for. number = UNDEFINED; is more meaningful than number = ‐1;

– provides easier program maintenance. We only need to change the value in the constant declaration instead of locating all occurrences of the same value in the program code


A Sample Use of Constantsclass Dice {

private static final int MAX_NUMBER = 6;private static final int MIN_NUMBER = 1;private static final int NO_NUMBER = 0;

private int number;

public Dice( ) {number = NO NUMBER;


number = NO_NUMBER;}

//Rolls the dicepublic void roll( ) {

number = (int) (Math.floor(Math.random() * (MAX_NUMBER - MIN_NUMBER + 1)) +

MIN_NUMBER);}

//Returns the number on this dicepublic int getNumber( ) {

return number;}

}

69

Local Variables• Local variables are declared within a method declaration and used for temporary services, such as storing intermediate computation results.

public double convert(int num) {


double result;

result = Math.sqrt(num * num);

return result; }

local variable

Local, Parameter & Data Member

• An identifier appearing inside a method can be a local variable, a parameter, or a data member.

• The rules are– If there’s a matching local variable declaration or a parameter, then the identifier refers to the local variable or the parameter.

– Otherwise, if there’s a matching data member declaration, then the identifier refers to the data member.

– Otherwise, it is an error because there’s no matching declaration.


Sample Matching

class MusicCD {

private String artist;private String title;private String id;

public MusicCD(String name1, String name2) {

String ident;


artist = name1;

title = name2;

ident = artist.substring(0,2) + "-" +

title.substring(0,9);

id = ident;}...

}

Calling Methods of the Same Class• So far, we have been calling a method of another class (object).

• It is possible to call method of a class from another method of the same class.– in this case, we simply refer to a method without dot notation


Changing Any Class to a Main Class• Any class can be set to be a main class.

• All you have to do is to include the main method.

class Bicycle {

//definition of the class as shown before


//comes here//The main method that shows a sample//use of the Bicycle classpublic static void main(String[] args) {

Bicycle myBike;myBike = new Bicycle( );myBike.setOwnerName("Jon Java");System.out.println(myBike.getOwnerName()

+ "owns a bicycle"); }

}

Chapter 5

Selection Statements


Animated Version

70

Objectives


• Implement a selection control using if statements

• Implement a selection control using switch statements• Implement a selection control using switch statements

• Write boolean expressions using relational and boolean expressions

• Evaluate given boolean expressions correctly

• Nest an if statement inside another if statement

• Describe how objects are compared

• Choose the appropriate selection control statement for a given task

The if Statement

int testScore;

testScore = //get test score input

if (testScore < 70)

JOptionPane.showMessageDialog(null, This statement is executed if the testScoreis less than 70.


"You did not pass" );

else

JOptionPane.showMessageDialog(null,

"You did pass" );

This statement is executed if the testScoreis 70 or higher.

Syntax for the if Statementif ( <boolean expression> )

<then block>

else

<else block>Boolean Expression


if ( testScore < 70 )

JOptionPane.showMessageDialog(null,"You did not pass" );

else

JOptionPane.showMessageDialog(null,"You did pass " );

Then Block

Else Block

Control Flow

JOptionPane.showMessageDialog

falsetestScore < 70 ?

JOptionPane.showMessageDialog

true


s o essage a og(null, "You did pass");

s o essage a og(null, "You did not pass");

Relational Operators< //less than

<= //less than or equal to

== //equal to

!= //not equal to

> //greater than

>= //greater than or equal to


testScore < 80

testScore * 2 >= 350

30 < w / (h * h)

x + y != 2 * (a + b)

2 * Math.PI * radius <= 359.99

Compound Statements• Use braces if the <then> or <else> block has multiple statements.

if (testScore < 70)

{

JOptionPane.showMessageDialog(null,"You did not pass“ );

JOptionPane.showMessageDialog(null, Then Block


JOpt o a e.s o essage a og( u ,“Try harder next time“ );

}

else

{

JOptionPane.showMessageDialog(null, “You did pass“ );

JOptionPane.showMessageDialog(null, “Keep up the good work“ );

}

Else Block

71

Style Guideif ( <boolean expression> ) {

…

}

else {

…

}

Style 1


if ( <boolean expression> )

{

…

}

else

{

…

}

Style 2

The if‐then Statementif ( <boolean expression> )

<then block>

Boolean Expression


if ( testScore >= 95 )

JOptionPane.showMessageDialog(null,"You are an honor student");

Then Block

Control Flow of if‐then

testScore >= 95?

JOptionPane.showMessageDialog (null,

true


falses o essage a og ( u ,"You are an honor student");

The Nested‐if Statement• The then and else block of an if statement can contain any valid statements, including other if statements. An if statement containing another if statement is called a nested‐if statement.

if (testScore >= 70) {


( ) {

if (studentAge < 10) {

System.out.println("You did a great job");

} else {

System.out.println("You did pass"); //test score >= 70

} //and age >= 10

} else { //test score < 70

System.out.println("You did not pass");

}

Control Flow of Nested‐if Statement

messageBox.show("You did not pass");

false inner if

false

testScore >= 70 ?

true

studentAge < 10 ?

true


messageBox.show("You did pass");

messageBox.show("You did a great job");

Writing a Proper if Controlif (num1 < 0)

if (num2 < 0)

if (num3 < 0)

negativeCount = 3;

else

negativeCount = 2;

else

if (num3 < 0)

negativeCount = 2;

else

negativeCount = 0;

if (num1 < 0)

negativeCount++;

if (num2 < 0)

negativeCount++;

if (num3 < 0)

negativeCount++;


negativeCount = 1;

else

if (num2 < 0)

if (num3 < 0)

negativeCount = 2;

else

negativeCount = 1;

else

if (num3 < 0)

negativeCount = 1;

else

negativeCount = 0;

The statement

negativeCount++;

increments the variable by one

72

if – else if Controlif (score >= 90)

System.out.print("Your grade is A");

else if (score >= 80)

System.out.print("Your grade is B");


Test Score Grade90 score A

80 score 90 B


System.out.print("Your grade is C");


System.out.print("Your grade is D");

else

System.out.print("Your grade is F");

80 score 90 B

70 score 80 C

60 score 70 D

score 60 F

Matching else

if (x < y)

if (x < z)

System.out.print("Hello");

else

System.out.print("Good bye");

A

Are and different?A B

if (x < y) {

if (x < z) {


Both and means…A B


if (x < y)

if (x < z)


else


B

} else {


}

}

Boolean Operators

• A boolean operator takes boolean values as its operands and returns a boolean value.

• The three boolean operators are– and: &&

||– or: ||

– not !


if (temperature >= 65 && distanceToDestination < 2) {System.out.println("Let's walk");

} else {System.out.println("Let's drive");

}

Semantics of Boolean Operators

• Boolean operators and their meanings:

P Q P && Q P || Q !P

false false false false true

false true false true true


false true false true true

true false false true false

true true true true false

De Morgan's Law

• De Morgan's Law allows us to rewrite boolean expressions in different ways

Rule 1: !(P && Q) !P || !Q

Rule 2: !(P || Q) !P && !Q


( || Q) Q

!(temp >= 65 && dist < 2)

!(temp >=65) || !(dist < 2) by Rule 1

(temp < 65 || dist >= 2)

Short‐Circuit Evaluation

• Consider the following boolean expression:

x > y || x > z

• The expression is evaluated left to right. If x > y is true, then there’s no need to evaluate x > z because the whole expression will be true whether x > z is true or notexpression will be true whether x > z is true or not.

• To stop the evaluation once the result of the whole expression is known is called short‐circuit evaluation.

• What would happen if the short‐circuit evaluation is not done for the following expression?

z == 0 || x / z > 20


73

Operator Precedence Rules


Boolean Variables

• The result of a boolean expression is either true or false. These are the two values of data type boolean.

• We can declare a variable of data type b l d i b l l iboolean and assign a boolean value to it.


boolean pass, done;pass = 70 < x;done = true;if (pass) {

…} else {

…}

Boolean Methods• A method that returns a boolean value, such as

private boolean isValid(int value) {if (value < MAX_ALLOWED)

return true;} else {

return false;


}}

Can be used as

if (isValid(30)) {…

} else {…

}

Comparing Objects

• With primitive data types, we have only one way to compare them, but with objects (reference data type), we have two ways to compare themcompare them.

1. We can test whether two variables point to the same object (use ==), or

2. We can test whether two distinct objects have the same contents.


Using == With Objects (Sample 1)

String str1 = new String("Java");String str2 = new String("Java");

if (str1 == str2) {System.out.println("They are equal");

} else {System.out.println("They are not equal");


y p ( y q )}

They are not equal Not equal because str1 and str2 point to different String objects.

Using == With Objects (Sample 2)

String str1 = new String("Java");String str2 = str1;

if (str1 == str2) {System.out.println("They are equal");

} else {System.out.println("They are not equal");


y p ( y q )}

They are equal It's equal here because str1 and str2 point to the same object.

74

Using equals with String

String str1 = new String("Java");String str2 = new String("Java");

if (str1.equals(str2)) {System.out.println("They are equal");

} else {S t t i tl ("Th t l")


System.out.println("They are not equal");}

They are equal It's equal here because str1 and str2 have the same sequence of characters.

The Semantics of ==


In Creating String Objects


The switch Statementint gradeLevel;

gradeLevel = Integer.parseInt( JOptionPane.showInputDialog("Grade (Frosh-1,Soph-2,...):" ) );

switch (gradeLevel) {

case 1: System.out.print("Go to the Gymnasium");

break;

case 2: System.out.print("Go to the Science Auditorium");

break;

This statement is executed if the gradeLevelis equal to 1.


break;

case 3: System.out.print("Go to Harris Hall Rm A3");

break;

case 4: System.out.print("Go to Bolt Hall Rm 101");

break;

}

This statement is executed if the gradeLevelis equal to 4.

Syntax for the switch Statement

switch ( gradeLevel ) {

switch ( <arithmetic expression> ) {

<case label 1> : <case body 1>

…

<case label n> : <case body n>

}Arithmetic Expression


case 1: System.out.print( "Go to the Gymnasium" );

break;

case 2: System.out.print( "Go to the Science Auditorium" );

break;

case 3: System.out.print( "Go to Harris Hall Rm A3" );

break;

case 4: System.out.print( "Go to Bolt Hall Rm 101" );

break;

}

Case Body

Case Label

switch With No break Statements

switch ( N ) {

case 1: x = 10;

case 2: x = 20;

x = 10;

false

trueN == 1 ?

N ==true


case 3: x = 30;

}

x = 20;

x = 30;

N 2 ?

N == 3 ?

false

falsetrue

75

switch With break Statements

switch ( N ) {

case 1: x = 10;

break;

case 2: x = 20;

x = 10;

false

trueN == 1 ?

N ==true

break;


break;

case 3: x = 30;

break;

}

x = 20;

x = 30;

N == 2 ?

N == 3 ?

false

falsetrue

break;

break;

switch With the default Blockswitch (ranking) {

case 10:

case 9:

case 8: System.out.print("Master");

break;

case 7:

6


case 6: System.out.print("Journeyman");

break;

case 5:

case 4: System.out.print("Apprentice");

break;

default: System.out.print("Input error: Invalid

Data");

break;

}

Chapter 6

Repetition Statements

©The McGraw-Hill Companies, Inc. Permission required for reproduction or

display.4th Ed Chapter 6 - 447

Animated Version


– Implement repetition control in a program using while statements.– Implement repetition control in a program using do‐while

statements.– Implement a generic loop‐and‐a‐half repetition control statement– Implement repetition control in a program using for statements.– Nest a loop repetition statement inside another repetition

statement.– Choose the appropriate repetition control statement for a given

task– Prompt the user for a yes‐no reply using the showConfirmDialog

method of JOptionPane.– (Optional) Write simple recursive methods

Definition• Repetition statements control a block of

code to be executed for a fixed number of times or until a certain condition is met.

• Count‐controlled repetitions terminate the execution of the block after it is executed for a fixed number of timesfor a fixed number of times.

• Sentinel‐controlled repetitions terminate the execution of the block after one of the designated values called a sentinel is encountered.

• Repetition statements are called loop statements also.



The while Statement

int sum = 0, number = 1;

while ( number <= 100 ) {

sum = sum + number; These statements are executed as long as number is less than or



number = number + 1;

}

number is less than or equal to 100.

76

Syntax for the while Statementwhile ( <boolean expression> )

<statement>Boolean Expression



while ( number <= 100 ) {

sum = sum + number;


}

Statement(loop body)

Control Flow of while

int sum = 0, number = 1

number <= true



number <= 100 ?

falsesum = sum + number;


More ExamplesKeeps adding the numbers 1, 2, 3, … until the sum becomes larger than 1,000,000.


while ( sum <= 1000000 ) {

sum = sum + number;


}

1

2



Computes the product of the first 20 odd integers.

int product = 1, number = 1,count = 20, lastNumber;

lastNumber = 2 * count - 1;

while (number <= lastNumber) {

product = product * number;


}

2

Finding GCD



Direct Approach More Efficient Approach

Example: Testing Input DataString inputStr;int age;

inputStr = JOptionPane.showInputDialog(null,"Your Age (between 0 and 130):");


while (age < 0 || age > 130) {

Priming Read



while (age < 0 || age > 130) {JOptionPane.showMessageDialog(null,

"An invalid age was entered. Please try again.");

inputStr = JOptionPane.showInputDialog(null,"Your Age (between 0 and 130):");

age = Integer.parseInt(inputStr); }

Useful Shorthand Operatorssum = sum + number; sum += number;is equivalent to

Operator Usage Meaning



+= a += b; a = a + b;

-= a -= b; a = a – b;

*= a *= b; a = a * b;

/= a /= b; a = a / b;

%= a %= b; a = a % b;

77

Watch Out for Pitfalls1. Watch out for the off‐by‐one error (OBOE).

2. Make sure the loop body contains a statement that will eventually cause the loop to terminate.

3. Make sure the loop repeats exactly the correct number of times.

4. If you want to execute the loop body N times, then initialize the counter to 0 and use the test condition counter < N or initialize the counter to 1 and use the test condition counter <= N.



Loop Pitfall ‐ 1

Infinite LoopsBoth loops will not

int product = 0;

while ( product < 500000 ) {

product = product * 5;

}

1

Both loops will not terminate because the boolean expressions will never become false.int count = 1;

while ( count != 10 ) {

count = count + 2;

}

2

Overflow

• An infinite loop often results in an overflow error.

• An overflow error occurs when you attempt to assign a value larger than the maximum value the variable can holdvalue the variable can hold.

• In Java, an overflow does not cause program termination. With types float and double, a value that represents infinity is assigned to the variable. With type int, the value “wraps around” and becomes a negative value.



Loop Pitfall ‐ 2float count = 0.0f;

while ( count != 1.0f ) {

count = count + 0.3333333f;

} //seven 3s

1

Using Real NumbersLoop 2 terminates, but Loop 1 does not because only an approximation of a real



float count = 0.0f;

while ( count != 1.0f ) {

count = count + 0.33333333f;

} //eight 3s

2

number can be stored in a computer memory.

Loop Pitfall – 2aint result = 0; double cnt = 1.0;

while (cnt <= 10.0){

cnt += 1.0;

result++;

}

System.out.println(result);

1

Using Real NumbersLoop 1 prints out 10, as 10



int result = 0; double cnt = 0.0;

while (cnt <= 1.0){

cnt += 0.1;

result++;

}

System.out.println(result);

2

expected, but Loop 2 prints out 11. The value 0.1 cannot be stored precisely in computer memory.

11

Loop Pitfall ‐ 3• Goal: Execute the loop body 10 times.

count = 1;while ( count < 10 ){

. . .count++;

}

1 count = 1;while (count <= 10 ){

. . .count++;

}

2



count = 0;while (count <= 10 ){

. . .count++;

}

3 count = 0;while (count < 10 ){

. . .count++;

}

4

1 3and exhibit off-by-one error.

78

The do‐while Statement


do {

sum += number;These statements are executed as long as sum



number++;

} while ( sum <= 1000000 );

gis less than or equal to 1,000,000.

Syntax for the do‐while Statement

do {

do<statement>

while (<boolean expression>);



sum += number;number++;

}while (sum<=1000000);


Boolean Expression

Control Flow of do‐while

int sum = 0, number = 1

sum += number;



number++;

sum <= 1000000 ?

true

false

Loop‐and‐a‐Half Repetition Control

• Loop‐and‐a‐half repetition control can be used to test a loop’s terminating condition in the middle of the loop body.

• It is implemented by using reserved words while, if, and break.



Example: Loop‐and‐a‐Half Control

String name;

while (true){

name = JOptionPane.showInputDialog(null,"Your name");



);

if (name.length() > 0) break;

JOptionPane.showMessageDialog(null, "Invalid Entry." + "You must enter at least one character.");

}

Pitfalls for Loop‐and‐a‐Half Control

• Be aware of two concerns when using the loop‐and‐a‐half control:– The danger of an infinite loop. The boolean expression of the while

statement is true, which will always evaluate to true. If we forget to include an if statement to break out of the loop it will result in aninclude an if statement to break out of the loop, it will result in an infinite loop.

– Multiple exit points. It is possible, although complex, to write a correct control loop with multiple exit points (breaks). It is good

practice to enforce the one‐entry one‐exit control flow.



79

Confirmation Dialog

• A confirmation dialog can be used to prompt the user to determine whether to continue a repetition or not.

JOptionPane.showConfirmDialog(null,

/*prompt*/ "Play Another Game?",

/*dialog title*/ "Confirmation",



/ g / ,

/*button options*/ JOptionPane.YES_NO_OPTION);

Example: Confirmation Dialog

boolean keepPlaying = true;int selection;

while (keepPlaying){

//code to play one game comes here// . . .

l ti JO ti P h C fi Di l (



selection = JOptionPane.showConfirmDialog( null,"Play Another Game?","Confirmation",JOptionPane.YES_NO_OPTION);

keepPlaying=(selection==JOptionPane.YES_OPTION);

}

The for Statement

int i, sum = 0, number;

for (i = 0; i < 20; i++) {

number = scanner.nextInt( );

sum += number;



sum += number;

}These statements are executed for 20 times( i = 0, 1, 2, … , 19).

Syntax for the for Statementfor ( <initialization>; <boolean expression>; <increment> )

<statement>

InitializationBoolean

ExpressionIncrement



for ( i = 0 ; i < 20 ; i++ ) {

number = scanner.nextInt();

sum += number;

}


Control Flow of for

i = 0;

falsei < 20 ?



number = . . . ;sum += number;

true

i ++;

More for Loop Examplesfor (int i = 0; i < 100; i += 5)1

i = 0, 5, 10, … , 95

for (int j = 2; j < 40; j *= 2)2



j = 2, 4, 8, 16, 32

for (int k = 100; k > 0; k--) )3

k = 100, 99, 98, 97, ..., 1

80

The Nested‐for Statement• Nesting a for statement inside another for statement is commonly used technique in programming.

• Let’s generate the following table using nested‐for statement.



Generating the Table

int price;

for (int width = 11; width <=20, width++){

for (int length = 5, length <=25, length+=5){

price = width * length * 19; //$19 per sq ftR



price = width * length * 19; //$19 per sq. ft.

System.out.print (" " + price);

}

//finished one row; move on to next row

System.out.println("");

}

INN

ER

OU

TER

Formatting Output

• We call the space occupied by an output value the field. The number of characters allocated to a field is the field width. The diagram shows the field width of 6.

• From Java 5.0, we can use the Formatter class. System.out(PrintStream) also includes the format method.



The Formatter Class

• We use the Formatter class to format the output.

• First we create an instance of the class

Formatter formatter = new Formatter(System.out);

• Then we call its format method

int num = 467;

formatter.format("%6d", num);

• This will output the value with the field width of 6.



The format Method of Formatter• The general syntax is

format(<control string>, <expr1>, <expr2>, . . . )

Example:int num1 = 34, num2 = 9;int num3 = num1 + num2;formatter.format("%3d + %3d = %5d", num1, num2, num3);



The format Method of PrintStream

• Instead of using the Formatter class directly, we can achieve the same result by using the format method of PrintStream (System.out)

Formatter formatter = new Formatter(System.out);formatter.format("%6d", 498);

is equivalent to

System.out.format("%6d", 498);



81

Control Strings

• Integers% <field width> d

• Real Numbers% <field width> . <decimal places> f

• Strings% s

• For other data types and more formatting options, please consult the Java API for the Formatter class.



Estimating the Execution Time

• In many situations, we would like to know how long it took to execute a piece of code. For example,– Execution time of a loop statement that finds the greatest common divisor of two very large numbers, or

– Execution time of a loop statement to display all prime numbers between 1 and 100 million

• Execution time can be measured easily by using the Date class.



Using the Date Class

• Here's one way to measure the execution time

Date startTime = new Date();

//code you want to measure the execution time



Date endTime = new Date();

long elapsedTimeInMilliSec =

endTime.getTime() – startTime.getTime();

Chapter 7

Defining Your Own Classes

Part 2



Animated Version

Objectives

• After you have read and studied this chapter, you should be able to – Describe how objects are returned from methods

– Describe how the reserved word this is used

– Define overloaded methods and constructors

– Define class methods and variables

– Describe how the arguments are passed to the parameters using the pass‐by‐value scheme

– Document classes with javadoc comments

– Organize classes into a package

Returning an Object from a Method

• As we can return a primitive data value from a method, we can return an object from a method also.

• We return an object from a method we are• We return an object from a method, we are actually returning a reference (or an address) of an object.

– This means we are not returning a copy of an object, but only the reference of this object



82

Sample Object‐Returning Method

• Here's a sample method that returns an object:

public Fraction simplify( ) {

F ti i

Return type indicates the class of an object we're returning from the method.



Fraction simp;

int num = getNumberator();int denom = getDenominator();int gcd = gcd(num, denom);

simp = new Fraction(num/gcd, denom/gcd);

return simp;}

Return an instance of the Fraction class

A Sample Call to simplify

f1 = new Fraction(24, 36);

f2 = f1.simplify();

public Fraction simplify( ) {

int num = getNumerator();int denom = getDenominator();int gcd = gcd(num, denom);

Fraction simp = new Fraction(num/gcd, denom/gcd);

return simp;}

f1simp



: Fraction

numerator

denominator36

24

f2

simp

: Fraction

numerator

denominator3

2

A Sample Call to simplify (cont'd) public Fraction simplify( ) {

int num = getNumerator();int denom = getDenominator();int gcd = gcd(num, denom);

Fraction simp = newFraction(num/gcd, denom/gcd);

return simp;}

f1 = new Fraction(24, 26);

f2 = f1.simplify();

f1simp



: Fraction

numerator

denominator3

2

: Fraction

numerator

denominator36

24

f2

simp

: Fraction

numerator

denominator3

2The value of simp, which is a reference, is returned and assigned to f2.

Reserved Word this

• The reserved word this is called a self‐referencing pointerbecause it refers to an object from the object's method.

: Object

this



this

• The reserved word this can be used in three different ways. We will see all three uses in this chapter.

The Use of this in the add Method

public Fraction add(Fraction frac) {

int a, b, c, d;Fraction sum;

a = this.getNumerator(); //get the receiving



b = this.getDenominator(); //object's num and denom

c = frac.getNumerator(); //get frac's numd = frac.getDenominator(); //and denom

sum = new Fraction(a*d + b*c, b*d);

return sum;}

f3 = f1.add(f2)

Because f1 is the receiving object (we're calling f1's method), so the reserved word



this is referring to f1.

83

f3 = f2.add(f1)

This time, we're calling f2's method, so the reserved word this is referring to



this is referring to f2.

Using this to Refer to Data Members

• In the previous example, we showed the use of thisto call a method of a receiving object.

• It can be used to refer to a data member as well.

class Person {



class Person {

int age;

public void setAge(int val) {this.age = val;

}. . .

}

Overloaded Methods• Methods can share the same name as long as

– they have a different number of parameters (Rule 1) or

– their parameters are of different data types when the number of parameters is the same (Rule 2)



public void myMethod(int x, int y) { ... }

public void myMethod(int x) { ... } Rule 1

public void myMethod(double x) { ... }

public void myMethod(int x) { ... } Rule 2

Overloaded Constructor• The same rules apply for overloaded constructors

– this is how we can define more than one constructor to a class



public Person( ) { ... }

public Person(int age) { ... } Rule 1

public Pet(int age) { ... }

public Pet(String name) { ... } Rule 2

Constructors and this

• To call a constructor from another constructor

public Fraction( ) { //creates 0/1this(0, 1);

}

public Fraction(int number) { //creates number/1this(number, 1);

}

of the same class, we use the reserved word this.



public Fraction(Fraction frac) { //copy constructorthis(frac.getNumerator(),

frac.getDenominator());}

public Fraction(int num, int denom) {setNumerator(num);setDenominator(denom);

}

Class Methods

• We use the reserved word static to define a class method.

public static int gcd(int m, int n) {

//th d i l ti th E lid l ith



//the code implementing the Euclidean algorithm}

public static Fraction min(Fraction f1, Fraction f2) {

//convert to decimals and then compare

}

84

Call‐by‐Value Parameter Passing

• When a method is called,

– the value of the argument is passed to the matching parameter, and

– separate memory space is allocated to store this value.

• This way of passing the value of arguments is called a pass‐by‐value or call‐by‐value schemevalue or call by value scheme.

• Since separate memory space is allocated for each parameter during the execution of the method,

– the parameter is local to the method, and therefore

– changes made to the parameter will not affect the value of the corresponding argument.



Call‐by‐Value Exampleclass Tester {

public void myMethod(int one, double two ) {one = 25;two = 35.4;

}}



Tester tester;int x, y;tester = new Tester();x = 10;y = 20;tester.myMethod(x, y);System.out.println(x + " " + y);

produces10 20

Memory Allocation for Parameters



Memory Allocation for Parameters (cont'd)



Parameter Passing: Key Points

1. Arguments are passed to a method by using the pass‐by‐ value scheme.

2. Arguments are matched to the parameters from left to right.The data type of an argument must be assignment‐compatible with the data type of the matching parameter.

3. The number of arguments in the method call must match the number f h h d d fof parameters in the method definition.

4. Parameters and arguments do not have to have the same name.

5. Local copies, which are distinct from arguments,are created even if the parameters and arguments share the same name.

6. Parameters are input to a method, and they are local to the method.Changes made to the parameters will not affect the value of corresponding arguments.



Organizing Classes into a Package

• For a class A to use class B, their bytecode files must be located in the same directory.– This is not practical if we want to reuse programmer‐defined classes in many different programs

• The correct way to reuse programmer‐defined classes from many different programs is to place reusable classes in a package.

• A package is a Java class library.



85

Creating a Package• The following steps illustrate the process of creating a package name myutil that includes the Fraction class.1. Include the statement

package myutil;as the first statement of the source file for the Fraction class.

2 The class declaration must include the visibility modifier public as2. The class declaration must include the visibility modifier public as

public class Fraction {...

}3. Create a folder named myutil, the same name as the package name. In Java, the

package must have a one‐to‐one correspondence with the folder.4. Place the modified Fraction class into the myutil folder and compile it.5. Modify the CLASSPATH environment variable to include the folder that contains

the myutil folder.



Using Javadoc Comments

• Many of the programmer‐defined classes we design are intended to be used by other programmers. – It is, therefore, very important to provide meaningful documentation

to the client programmers so they can understand how to use our classes correctly.

• By adding javadoc comments to the classes we design, we can provide a consistent style of documenting the classes.

• Once the javadoc comments are added to a class, we can generate HTML files for documentation by using the javadoc command.



javadoc for Fraction

• This is a portion of the HTML documentation for the Fraction class shown in a browser.

• This HTML file is produced by processing the javadoc comments in the source file of the Fraction class.



javadoc Tags

• The javadoc comments begins with /** and ends with */

• Special information such as the authors, parameters, return values, and others are p , ,indicated by the @ marker

@param

@author

@return

etc



Example: javadoc Source

. . .

/*** Returns the sum of this Fraction* and the parameter frac. The sum* returned is NOT simplified.** @ f th F ti t dd t thi this javadoc

©The McGraw-Hill Companies, Inc. Permission required for

reproduction or display.4th Ed Chapter 7 - 509

* @param frac the Fraction to add to this* Fraction** @return the sum of this and frac*/public Fraction add(Fraction frac) {

...}. . .

this javadocwill produce

Example: javadoc Output



86

javadoc Resources

• General information on javadoc is located at

http://java.sun.com/j2se/javadoc

• Detailed reference on how to use javadoc on Windows is located at

http://java.sun.com/j2se/1.5/docs/tooldocs/windows/javadoc.html



Chapter 8

Exceptions and Assertions



Objectives

• After you have read and studied this chapter, you should be able to

– Improve the reliability of code by incorporating exception‐handling and assertion mechanisms.exception handling and assertion mechanisms.

– Write methods that propagate exceptions.

– Implement the try‐catch blocks for catching and handling exceptions.

– Write programmer‐defined exception classes.

– Distinguish the checked and unchecked, or runtime, exceptions.

Definition

• An exception represents an error condition that can occur during the normal course of program execution.



• When an exception occurs, or is thrown, the normal sequence of flow is terminated. The exception‐handling routine is then executed; we say the thrown exception is caught.

Not Catching Exceptions

String inputStr;

int age;

inputStr = JOptionPane.showInputDialog(null, "Age:");




java.lang.NumberFormatException: tenat java.lang.Integer.parseInt(Integer.java:405)at java.lang.Integer.parseInt(Integer.java:454)at Ch8Sample1.main(Ch8Sample1.java:20)

Error message for invalid input

Catching an Exception

inputStr = JOptionPane.showInputDialog(null, "Age:");

try {

age = Integer.parseInt(inputStr);try



} catch (NumberFormatException e){

JOptionPane.showMessageDialog(null, "’" + inputStr

+ "‘ is invalid\n"

+ "Please enter digits only");

}

catch

87

try‐catch Control Flow



Getting Information

• There are two methods we can call to get information about the thrown exception:

– getMessage

printStackTrace



– printStackTracetry {

. . .


System.out.println(e.getMessage());

System.out.println(e.printStackTrace());

}

Multiple catch Blocks• A single try‐catch statement can include multiple catch blocks,

one for each type of exception.

try {

. . .


. . .



val = cal.get(id); //cal is a GregorianCalendar

. . .


. . .

} catch (ArrayIndexOutOfBoundsException e){

. . .

}

Multiple catch Control Flow



The finally Block

• There are situations where we need to take certain actions regardless of whether an exception is thrown or not.

• We place statements that must be executed



• We place statements that must be executed regardless of exceptions in the finally block.

try‐catch‐finally Control Flow



88

Propagating Exceptions• Instead of catching a thrown exception by using the try‐

catch statement, we can propagate the thrown exception back to the caller of our method.

• The method header includes the reserved word throws.



public int getAge( ) throws NumberFormatException {

. . .

int age = Integer.parseInt(inputStr);

. . .

return age;

}

Throwing Exceptions• We can write a method that throws an exception directly,

i.e., this method is the origin of the exception.

• Use the throw reserved to create a new instance of the Exception or its subclasses.

• The method header includes the reserved word throws.



public void doWork(int num) throws Exception {

. . .

if (num != val) throw new Exception("Invalid val");

. . .

}

Exception Thrower

• When a method may throw an exception, either directly or indirectly, we call the method an exception thrower.



• Every exception thrower must be one of two types:– catcher.

– propagator.

Types of Exception Throwers

• An exception catcher is an exception thrower that includes a matching catch block for the thrown exception.



• An exception propagator does not contain a matching catch block.

• A method may be a catcher of one exception and a propagator of another.

Sample Call Sequence



Exception Types

• All types of thrown errors are instances of the Throwable class or its subclasses.

• Serious errors are represented by instances of the Error class or its subclasses.



• Exceptional cases that common applications should handle are represented by instances of the Exception class or its subclasses.

89

Throwable Hierarchy

• There are over 60 classes in the hierarchy.



Checked vs. Runtime

• There are two types of exceptions:– Checked.

– Unchecked.

• A checked exception is an exception that is



checked at compile time.

• All other exceptions are unchecked, or runtime, exceptions. As the name suggests, they are detected only at runtime.

Different Handling Rules

• When calling a method that can throw checked exceptions – use the try‐catch statement and place the call in the try block, or



– modify the method header to include the appropriate throws clause.

• When calling a method that can throw runtime exceptions, it is optional to use the try‐catch statement or modify the method header to include a throws clause.

Handling Checked Exceptions



Handling Runtime Exceptions



Programmer‐Defined Exceptions

• Using the standard exception classes, we can use the getMessage method to retrieve the error message.

• By defining our own exception class, we can pack more useful information

– for example we may define a OutOfStock exception class and include



for example, we may define a OutOfStock exception class and include information such as how many items to order

• AgeInputException is defined as a subclass of Exception and includes public methods to access three pieces of information it carries: lower and upper bounds of valid age input and the (invalid) value entered by the user.

90

Assertions

• The syntax for the assert statement is

assert <boolean expression>;



where <boolean expression>represents the condition that must be true if the code is working correctly.

• If the expression results in false, an AssertionError (a subclass of Error) is thrown.

Sample Use #1

public double deposit(double amount) {double oldBalance = balance;balance += amount;assert balance > oldBalance;

}



public double withdraw(double amount) {double oldBalance = balance;balance -= amount;assert balance < oldBalance;

}

Second Form

• The assert statement may also take the form:

assert <boolean expression>: <expression>;



where <expression> represents the value passed as an argument to the constructor of the AssertionError class. The value serves as the detailed message of a thrown exception.

Sample Use #2

public double deposit(double amount) {

double oldBalance = balance;

balance += amount;



balance + amount;

assert balance > oldBalance :"Serious Error – balance did not " +" increase after deposit";

}

Compiling Programs with Assertions

• Before Java 2 SDK 1.4, the word assert is a valid nonreserved identifier. In version 1.4 and after, the word assert is treated as a regular identifier to ensure compatibility



identifier to ensure compatibility.

• To enable the assertion mechanism, compile the source file using

javac –source 1.4 <source file>

Running Programs with Assertions

• To run the program with assertions enabled, use

java –ea <main class>



j

• If the –ea option is not provided, the program is executed without checking assertions.

91

Different Uses of Assertions

• Precondition assertions check for a condition that must be true before executing a method.

• Postcondition assertions check conditions that must be true after a method is executed



must be true after a method is executed.

• A control‐flow invariant is a third type of assertion that is used to assert the control must flow to particular cases.

Chapter 9

Characters and Strings



Objectives

• After you have read and studied this chapter, you should be able to – Declare and manipulate data of the char data type.– Write string processing program using String, StringBuilder and StringBuffer objectsStringBuilder, and StringBuffer objects.

– Differentiate the three string classes and use the correct class for a given task.

– Specify regular expressions for searching a pattern in a string.

– Use the Pattern and Matcher classes.– Compare the String objects correctly.

Characters

• In Java, single characters are represented using the data type char.

• Character constants are written as symbols enclosed in single quotes.

• Characters are stored in a computer f f dmemory using some form of encoding.

• ASCII, which stands for American Standard Code for Information Interchange, is one of the document coding schemes widely used today.

• Java uses Unicode, which includes ASCII, for representing char constants.



ASCII Encoding

9



For example, character 'O' is 79 (row value 70 + col value 9= 79).

O70

Unicode Encoding

• The Unicode Worldwide Character Standard(Unicode) supports the interchange, processing, and display of the written texts of diverse languages.

• Java uses the Unicode standard for representing char constants.

char ch1 = 'X';

System.out.println(ch1);System.out.println( (int) ch1);

X88

92

Character ProcessingDeclaration and initialization

char ch1, ch2 = ‘X’;

Type conversion between

System.out.print("ASCII code of character X is " + (int) 'X' );



int and char.System.out.print("Character with ASCII code 88 is " + (char)88 );

This comparison returns true because ASCII value of 'A' is 65 while that of 'c'is 99.

‘A’ < ‘c’

Strings

• A string is a sequence of characters that is treated as a single value.

• Instances of the String class are used to represent strings in Javarepresent strings in Java.

• We can access individual characters of a string by calling the charAt method of the Stringobject.



Accessing Individual Elements• Individual characters in a String accessed with the charAt

method.

String name = "Sumatra";



0 1 2 3 4 5 6

S u m a t r a

nameThis variable refers to the whole string.

name.charAt( 3 )The method returns the character at position # 3.

Example: Counting Vowelschar letter;

String name = JOptionPane.showInputDialog(null,"Your name:");

int numberOfCharacters = name.length();

int vowelCount = 0;

for (int i = 0; i < numberOfCharacters; i++) {

letter = name.charAt(i);

if ( l tt ' ' || l tt 'A' ||

Here’s the code to count the number of vowels in the input string.



if ( letter == 'a' || letter == 'A' ||

letter == 'e' || letter == 'E' ||

letter == 'i' || letter == 'I' ||

letter == 'o' || letter == 'O' ||

letter == 'u' || letter == 'U' ) {

vowelCount++;

}

}

System.out.print(name + ", your name has " + vowelCount + " vowels");

g

Example: Counting ‘Java’ int javaCount = 0;

boolean repeat = true;

String word;

while ( repeat ) {

word = JOptionPane.showInputDialog(null,"Next word:");

Continue reading words and count how many times the word Java occurs in the input, ignoring the case.



if ( word.equals("STOP") ) {

repeat = false;

} else if ( word.equalsIgnoreCase("Java") ) {

javaCount++;

}

}

Notice how the comparison is done. We are not using the == operator.

Other Useful String OperatorsMethod Meaning

compareTo Compares the two strings.str1.compareTo( str2 )

substring Extracts the a substring from a string.str1.substring( 1, 4 )

trim Removes the leading and trailing spaces.str1 trim( )



str1.trim( )

valueOf Converts a given primitive data value to a string.String.valueOf( 123.4565 )

startsWith Returns true if a string starts with a specified prefix string.str1.startsWith( str2 )

endsWith Returns true if a string ends with a specified suffix string.str1.endsWith( str2 )

• See the String class documentation for details.

93

Pattern Example• Suppose students are assigned a three‐digit code:

– The first digit represents the major (5 indicates computer science);

– The second digit represents either in‐state (1), out‐of‐state (2), or foreign (3);

– The third digit indicates campus housing:

• On‐campus dorms are numbered 1‐7.

d l ff d b h d• Students living off‐campus are represented by the digit 8.



The 3-digit pattern to represent computer science majors living on-campus is

5[123][1-7]

firstcharacter

is 5second

characteris 1, 2, or 3

thirdcharacter

is any digit between 1 and 7

Regular Expressions

• The pattern is called a regular expression.

• Rules– The brackets [ ] represent choices

– The asterisk symbol * means zero or more occurrences.

– The plus symbol + means one or more occurrences.

– The hat symbol ^ means negation.

– The hyphen – means ranges.

– The parentheses ( ) and the vertical bar | mean a range of choices for multiple characters.



Regular Expression Examples

Expression Description[013] A single digit 0, 1, or 3.

[0-9][0-9] Any two-digit number from 00 to 99.

[0-9&&[^4567]] A single digit that is 0, 1, 2, 3, 8, or 9.

[a-z0-9] A single character that is either a lowercase letter or a digit.g

[a-zA-Z][a-zA-Z0-9_$]*

A valid Java identifier consisting of alphanumeric characters, underscores, and dollar signs, with the first character being an alphabet.

[wb](ad|eed) Matches wad, weed, bad, and beed.

(AZ|CA|CO)[0-9][0-9] Matches AZxx,CAxx, and COxx, where x is a single digit.



The replaceAll Method• The replaceAll method replaces all occurrences of a substring that matches a given regular expression with a given replacement string.

Replace all vowels with the symbol @



String originalText, modifiedText;

originalText = ...; //assign string

modifiedText = originalText.replaceAll("[aeiou]","@");

The Pattern and Matcher Classes

• The matches and replaceAll methods of the String class are shorthand for using the Pattern and Matcher classes from the java.util.regex package.

• If str and regex are String objects, then

str.matches(regex);g

is equivalent to

Pattern pattern = Pattern.compile(regex);

Matcher matcher = pattern.matcher(str);

matcher.matches();



The compile Method• The compile method of the Pattern class converts the stated regular expression to an internal format to carry out the pattern‐matching operation.

• This conversion is carried out every time the matches method of the String class is executed, so it is more efficient to use the compile method when we search for the same pattern multiple times.

• See the sample programs Ch9MatchJavaIdentifier2 and Ch9PMCountJava



94

The find Method

• The find method is another powerful method of the Matcher class.– It searches for the next sequence in a string that matches the pattern, and returns true if the pattern is foundfound.

• When a matcher finds a matching sequence of characters, we can query the location of the sequence by using the start and end methods.

• See Ch9PMCountJava2



The String Class is Immutable

• In Java a String object is immutable– This means once a String object is created, it cannot be changed, such as replacing a character with another character or removing a character

– The String methods we have used so far do not change the original string. They created a new string from the original. For example, substring creates a new string from a given string.

• The String class is defined in this manner for efficiency reason.



Effect of Immutability



We can do thisbecause Stringobjects areimmutable.

The StringBuffer Class

• In many string processing applications, we would like to change the contents of a string. In other words, we want it to be mutable.

• Manipulating the content of a string such as• Manipulating the content of a string, such as replacing a character, appending a string with another string, deleting a portion of a string, and so on, may be accomplished by using the StringBuffer class.



StringBuffer Example

Changing a string Java to Diva

word

: StringBuffer

Java

word

: StringBuffer

Diva



StringBuffer word = new StringBuffer("Java");word.setCharAt(0, 'D');word.setCharAt(1, 'i');

Before

Diva

After

Sample ProcessingReplace all vowels in the sentence with ‘X’.

char letter;

String inSentence = JOptionPane.showInputDialog(null, "Sentence:");

StringBuffer tempStringBuffer = new StringBuffer(inSentence);

int numberOfCharacters = tempStringBuffer.length();

for (int index = 0; index < numberOfCharacters; index++) {



letter = tempStringBuffer.charAt(index);

if ( letter == 'a' || letter == 'A' || letter == 'e' || letter == 'E' ||

letter == 'i' || letter == 'I' || letter == 'o' || letter == 'O' ||

letter == 'u' || letter == 'U' ) {

tempStringBuffer.setCharAt(index,'X');

}

}

JOptionPane.showMessageDialog(null, tempStringBuffer );

95

The append and insert Methods

• We use the append method to append a String or StringBuffer object to the end of a StringBuffer object. – The method can also take an argument of the primitive data type.

– Any primitive data type argument is converted to a string before it is appended to a StringBuffer object.

• We can insert a string at a specified position by using the insert method.



The StringBuilder Class

• This class is new to Java 5.0 (SDK 1.5)

• The class is added to the newest version of Java to improve the performance of the StringBuffer class.

• StringBuffer and StringBuilder support exactly the same set of methods so they are interchangeablemethods, so they are interchangeable.

• There are advanced cases where we must use StringBuffer, but all sample applications in the book, StringBuilder can be used.

• Since the performance is not our main concern and that the StringBuffer class is usable for all versions of Java, we will use StringBuffer only in this book.



Chapter 10

Arrays


Animated Version

Objectives

• After you have read and studied this chapter, you should be able to – Manipulate a collection of data values, using an array.– Declare and use an array of primitive data types in writing a program.Declare and use an array of objects in writing a– Declare and use an array of objects in writing a program

– Define a method that accepts an array as its parameter and a method that returns an array

– Describe how a two‐dimensional array is implemented as an array of arrays

– Manipulate a collection of objects, using lists and maps

Array Basics

• An array is a collection of data values.

• If your program needs to deal with 100 i 00 bj 36 lintegers, 500 Account objects, 365 real numbers, etc., you will use an array.

• In Java, an array is an indexed collection of data values of the same type.


Arrays of Primitive Data Types

• Array Declaration<data type> [ ] <variable> //variation 1

<data type> <variable>[ ] //variation 2

• Array Creation<variable> = new <data type> [ <size> ]

• ExampleExample


double[ ] rainfall;

rainfall

= new double[12];

Variation 1

double rainfall [ ];

rainfall

= new double[12];

Variation 2

An array is like an object!

96

Accessing Individual Elements• Individual elements in an array accessed with the indexed

expression.

double[] rainfall = new double[12];

rainfall0 1 2 3 4 5 6 7 8 9 10 11


The index of the firstposition in an array is 0.

0 1 2 3 4 5 6 7 8 9 10 11

rainfall[2]This indexed expression refers to the element at position #2

Array Processing – Sample1double[] rainfall = new double[12];

double annualAverage,

sum = 0.0;

for (int i = 0; i < rainfall.length; i++) {

rainfall[i] = Double.parseDouble(

The public constant length returns the capacity of an array.


JOptionPane.showInputDialog(null,

"Rainfall for month " + (i+1) ) );

sum += rainfall[i];

}

annualAverage = sum / rainfall.length;

Array Processing – Sample 2double[] rainfall = new double[12];

String[] monthName = new String[12];

monthName[0] = "January";

monthName[1] = "February";

…

double annualAverage, sum = 0.0;

The same pattern for the remaining ten months.


for (int i = 0; i < rainfall.length; i++) {

rainfall[i] = Double.parseDouble(

JOptionPane.showinputDialog(null, "Rainfall for "

+ monthName[i] ));

sum += rainfall[i];

}

annualAverage = sum / rainfall.length;The actual month name instead of a number.

Array Processing – Sample 3• Compute the average rainfall for each quarter.

//assume rainfall is declared and initialized properly

double[] quarterAverage = new double[4];


for (int i = 0; i < 4; i++) {

sum = 0;

for (int j = 0; j < 3; j++) { //compute the sum of

sum += rainfall[3*i + j]; //one quarter

}

quarterAverage[i] = sum / 3.0; //Quarter (i+1) average

}

Array Initialization• Like other data types, it is possible to declare and initialize an array at the same time.

int[] number = { 2, 4, 6, 8 };

double[] samplingData = { 2.443, 8.99, 12.3, 45.009, 18.2,9.00, 3.123, 22.084, 18.08 };


String[] monthName = { "January", "February", "March","April", "May", "June", "July","August", "September", "October","November", "December" };

number.lengthsamplingData.length

monthName.length

49

12

Variable‐size Declaration• In Java, we are not limited to fixed‐size array declaration.

• The following code prompts the user for the size of an array and declares an array of designated size:i t i


int size;

int[] number;

size= Integer.parseInt(JOptionPane.showInputDialog

(null, "Size of an array:"));

number = new int[size];

97

Arrays of Objects

• In Java, in addition to arrays of primitive data types, we can declare arrays of objects

• An array of primitive data is a powerful tool, but an array of objects is even more powerful.an array of objects is even more powerful.

• The use of an array of objects allows us to model the application more cleanly and logically.


The Person Class• We will use Person objects to illustrate the use of an array of

objects.

Person latte;

latte = new Person( );The Person class supports the set methods and get methods.


latte.setName("Ms. Latte");

latte.setAge(20);

latte.setGender('F');

System.out.println( "Name: " + latte.getName() );

System.out.println( "Age : " + latte.getAge() );

System.out.println( "Sex : " + latte.getGender() );

and get methods.

Creating an Object Array ‐ 1

Code Person[ ] myPerson;

myPerson = new Person[20];

myPerson[0] = new Person( );

AOnly the name myPerson is declared, no array is allocated yet.

myPerson


State of Memory

After is executedA


myPerson



myPerson[0] = new Person( );

BNow the array for storing 20 Person objects is created, but the Person objects themselves are not yet created.

myPerson


on

State of Memory

After is executedB

0 1 2 3 4 16 17 18 19




myPerson[0] = new Person( );C

One Person object is created and the reference to this object is placed in position 0.

myPersonmyPerson


State of Memory

0 1 2 3 4 16 17 18 19

on

0 1 2 3 4 16 17 18 19

After is executedC

Person

Person Array Processing – Sample 1• Create Person objects and set up the myPerson array.

String name, inpStr;

int age;

char gender;

for (int i = 0; i < myPerson.length; i++) {

name = inputBox.getString("Enter name:"); //read in data values

i ( )


age = inputBox.getInteger("Enter age:");

inpStr = inputBox.getString("Enter gender:");

gender = inpStr.charAt(0);

myPerson[i] = new Person( ); //create a new Person and assign values

myPerson[i].setName ( name );

myPerson[i].setAge ( age );

myPerson[i].setGender( gender );

}

98

Person Array Processing – Sample 2• Find the youngest and oldest persons.

int minIdx = 0; //index to the youngest myPerson

int maxIdx = 0; //index to the oldest myPerson

for (int i = 1; i < myPerson.length; i++) {

if ( myPerson[i].getAge() < myPerson[minIdx].getAge() ) {

//


minIdx = i; //found a younger myPerson

} else if (myPerson[i].getAge() > myPerson[maxIdx].getAge() ) {

maxIdx = i; //found an older myPerson

}

}

//myPerson[minIdx] is the youngest and myPerson[maxIdx] is the oldest

Object Deletion – Approach 1

int delIdx = 1;

myPerson[delIdx] = null;Delete Person B by setting the reference in position 1 to null.

myPerson

A

myPerson


0 1 2 3

A B C D

0 1 2 3

A C D

Before is executedA After is executedA

Object Deletion – Approach 2

int delIdx = 1, last = 3;

myPerson[delIdx] = myPerson[last];

myPerson[last] = null;

Delete Person B by setting the reference in position 1 to the last person.

myPerson

A

myPerson


0 1 2 3

A B C D

0 1 2 3

A CD

Before is executedA After is executedA

Person Array Processing – Sample 3• Searching for a particular person. Approach 2 Deletion is used.

int i = 0;

while ( myPerson[i] != null && !myPerson[i].getName().equals("Latte") ) {

i++;

}


if ( myPerson[i] == null ) {

//not found - unsuccessful search

System.out.println("Ms. Latte was not in the array");

} else {

//found - successful search

System.out.println("Found Ms. Latte at position " + i);

}

Passing Arrays to Methods ‐ 1CodeminOne = searchMinimum(arrayOne);

public int searchMinimum(float[] number)){

…

}

A


State of Memory

At before searchMinimumA

arrayOneA. Local variable number does not exist before the method execution



…

}

B


State of Memory

arrayOnearrayOne

The address is copied at B

numberB. The value of the argument, which is an address, is copied to the parameter.

99

Passing Arrays to Methods ‐ 3

Whil t i id th th dC

CodeminOne = searchMinimum(arrayOne);


…

}

C


arrayOne number

While at inside the methodC

State of Memory

C. The array is accessed via number inside the method.



…

}

D

hMi iD


arrayOne

At after searchMinimumD

number

State of Memory

D. The parameter is erased. The argument still points to the same object.

arrayOne

At after searchMinimumD

Two‐Dimensional Arrays• Two‐dimensional arrays are useful in representing tabular information.


Declaring and Creating a 2‐D Array

Declaration

<data type> [][] <variable> //variation 1<data type> <variable>[][] //variation 2

Creation

<variable> = new <data type> [ <size1> ][ <size2> ]


Example

double[][] payScaleTable;

payScaleTable

= new double[4][5];

3

2

1

0

43210payScaleTable

Accessing an Element• An element in a two‐dimensional array is accessed by its row and column index.


Sample 2‐D Array Processing• Find the average of each row.

double[ ] average = { 0.0, 0.0, 0.0, 0.0 };

for (int i = 0; i < payScaleTable.length; i++) {

for (int j = 0; j < payScaleTable[i].length; j++) {


average[i] += payScaleTable[i][j];

}

average[i] = average[i] / payScaleTable[i].length;

}

100

Java Implementation of 2‐D Arrays

• The sample array creation

payScaleTable = new double[4][5];

is really a shorthand foris really a shorthand for

payScaleTable = new double [4][ ];

payScaleTable[0] = new double [5];payScaleTable[1] = new double [5];payScaleTable[2] = new double [5];payScaleTable[3] = new double [5];

Two‐Dimensional Arrays

• Subarrays may be different lengths. • Executing

triangularArray = new double[4][ ];for (int i = 0; i < 4; i++)triangularArray[i] = new double [i + 1];

results in an array that looks like:


y

Lists and Maps

• The java.util standard package contains different types of classes for maintaining a collection of objects.

• These classes are collectively referred to as• These classes are collectively referred to as the Java Collection Framework (JCF).

• JCF includes classes that maintain collections of objects as sets, lists, or maps.


Java Interface

• A Java interface defines only the behavior of objects

– It includes only public methods with no method bodies.

– It does not include any data members except public constants

– No instances of a Java interface can be created


JCF Lists

• JCF includes the List interface that supports methods to maintain a collection of objects as a linear list

L = (l0, l1, l2, . . . , lN)

• We can add to, remove from, and retrieve objects in a given list.

• A list does not have a set limit to the number of objects we can add to it.


List Methods

• Here are five of the 25 list methods:

boolean add ( Object o )

Adds an object o to the list

void clear ( )

Clears this list i e make the list empty


Clears this list, i.e., make the list empty

Object get ( int idx )

Returns the element at position idx

boolean remove ( int idx )

Removes the element at position idx

int size ( )

Returns the number of elements in the list

101

Using Lists

• To use a list in a program, we must create an instance of a class that implements the List interface.

• Two classes that implement the List interface:– ArrayList

Li k dLi– LinkedList

• The ArrayList class uses an array to manage data.

• The LinkedList class uses a technique called linked‐node representation.


Sample List Usage• Here's an example of manipulating a list:

import java.util.*;

List friends;

Person myPerson;


friends = new ArrayList( );

myPerson = new Person("jane", 10, 'F');

friends.add( myPerson );

myPerson = new Person("jack", 6, 'M');

friends.add( myPerson );

Person p = (Person) friends.get( 1 );

JCF Maps

• JCF includes the Map interface that supports methods to maintain a collection of objects (key, value) pairs called map entries.

key value

k v one entry


k0

k1

kn

v0

v1

vn

.

.

.

.

.

.

one entry

Map Methods

• Here are five of the 14 list methods:

void clear ( )

Clears this list, i.e., make the map empty

boolean containsKey ( Object key )

Returns true if the map contains an entry with a given


Returns true if the map contains an entry with a given key

Object put (Object key, Object value)

Adds the given (key, value) entry to the map

boolean remove ( Object key )

Removes the entry with the given key from the map

int size ( )

Returns the number of elements in the map

Using Maps

• To use a map in a program, we must create an instance of a class that implements the Map interface.

• Two classes that implement the Mapfinterface:

– HashMap

– TreeMap


Sample Map Usage• Here's an example of manipulating a map:

import java.util.*;

Map catalog;

catalog = new TreeMap( );

catalog.put("CS101", "Intro Java Programming");catalog.put( CS101 , Intro Java Programming );

catalog.put("CS301", "Database Design");

catalog.put("CS413", "Software Design for Mobile Devices");

if (catalog.containsKey("CS101")) {

System.out.println("We teach Java this semester");

} else {

System.out.println("No Java courses this semester");

}

102

Database ProgrammingWith Java

Dr Stuart Kerrigan


• The components of the JDBC interface to DBMSs

• How to connect to a database from Java

• How to send SQL statements from Java to a DBMS

• The concepts of ResultSet object and a Cursor• The concepts of ResultSet object and a Cursor

• How to navigate and update a ResultSet from Java

608

JDBC

• JDBC is the Java Database Connectivity API– Allows Java program to access data stored in tabular format, such as in RDBMS and spreadsheets.

– DB driver written by the DB vendor and implemented as a class which is loaded prior to using the JDBCas a class which is loaded prior to using the JDBC methods it provides.

– Driver and supporting classes and information typically packaged in jar file.

– MySQL Connector/J

• JDBC is the driver for MySQL

609

The JDBC Programming Model

• The JDBC uses a client‐server programming model:– Client makes a connection to the

DB (the server)– Client sends SQL statement(s) to

the DBManipulate database metadata– Manipulate database metadata

– DB sends back a Result Set– Client processes Result Set– Client disconnects from the DB

• Points to note:– Result Set includes query results

and metadata– JDBC throws an exception

whenever there's an error

610

Using JDBC

• Import JDBC library– import java.sql.*;

• DriverManager provides DB interface methods• Most Java programs use import to load a class• With JDBC, usually load driver class at runtime:

import java.lang.*;p j gimport java.sql.*;public static void main (String args[]) {try { // this loads & initialises the driverClass.forName("com.mysql.jdbc.Driver");// now connect to DB ...} catch (ClassNotFoundException e) {

System.err.println(e.getMessage());e.printStackTrace();System.exit(1);

} }

611

What Does Try Mean?

• Errors always occur in software programs.

• Database programs may be critical applications.

• Errors should be caught and handled gracefully.

P h ld d l h d b• Programs should recover and leave the database in a consistent state.

• Use Java exception handlers to detect errors.

• Read Wu Chapter 8

612

103

Making a JDBC‐ODBCDatabase Connection

Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/mydatabase","yourusername", "yourpassword");// make more calls to JDBC methods here...con.close();

• Need to put your own username (typically root) and password (your MySQL password) into the getConnection method

613

Statement and ResultSet Objects

Statement stmt = con.createStatement();String sql = "SELECT * FROM Staff;";ResultSet rs = stmt.executeQuery(sql);print_rs(rs); // shown laterrs.close(); // free memorystmt close();stmt.close();

• Can pass any legal SQL query to executeQuery()

• Here, rs holds the entire results table (Staff)...

614

ResultSets and Cursors

• Each ResultSet contains:

– Numbered Fields (columns)

– Field names & types (metadata)

The ResultSet object is a ‘container’ for the results of a query (table):

– A Cursor (current row)

615

•First cursor position is BEFORE FIRST ROW• Rows and columns COUNT FROM ONE

ResultSet Metadata

• We can find the number of columns, the column names and data types (REAL, CHAR, etc.) from the ResultSet metadata:

ResultSetMetaData md = rs.getMetaData();int num columns = md.getColumnCount();int num_columns md.getColumnCount();for (int i=1; i<=num_columns; i++) {

System.out.println("Column Number = " + i);System.out.println("Column Name = " + md.getColumnLabel(i));System.out.println("Column Type = " + md.getColumnTypeName(i));

}

616

Example: Printing a ResultSet

• We can move through the rows using the next() method:private void print_rs(ResultSet rs) throwsSQLException {

ResultSetMetaData md = rs.getMetaData();int num_columns = md.getColumnCount();while (rs.next()) {

ffString row_buffer = "";for (int i=1; i<=num_columns; i++) {

row_buffer += row_buffer + " " + rs.getString(i);

}System.out.println(row_buffer);

} }

• Note use of metadata and getString() method

617

Handling ResultSet Field Types

• There is a ‘get’ function for each of the main SQL data types (each needs a column no. or a column name):– getString()

– getInt()

– getDouble()

D ()– getDate()

– in general getxxxx()

• To do arithmetic on field values, need to extract into appropriate type:– double ave = rs.getDouble("Rent") /rs.getInt("Rooms");

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Updatable & Scrollable Cursors

• There are several types of ‘cursor’. The type we get is controlled by the call to createStatement():stmt = con.createStatement(int scrolling, int concurrency);

• scrolling:– ResultSet.TYPE_FORWARD_ONLY ‐ the default!

– ResultSet.TYPE_SCROLL_INSENSITIVE ‐ use this

– ResultSet.TYPE_SCROLL_SENSITIVE ‐ advanced

• concurrency:– ResultSet.CONCUR_READ_ONLY ‐ the default!

– ResultSet.CONCUR_UPDATABLE

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Scrollable Cursor Method Functions

• Scrollable cursors have a rich set of method functions:– Boolean next(), previous()– void absolute(int row_num), – void relative(int row_increment),– Boolean first(), last()– void beforeFirst(), afterLast()

• You can also ask where the cursor is currently positioned:– Boolean isFirst(), isLast()– Boolean isBeforeFirst(), isAfterLast()

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Inserting or Deleting Rows

• For queries that do not return a ResultSet, use the executeUpdate() method:Statement stmt = con.createStatement();String sql = "DELETE FROM Client " +"WHERE ClientNo = " +"'CR56' ""'CR56';";int num_rows = stmt.executeUpdate(sql);

• If successful, get num_rows = 1 (no. rows changed)

• Could use "INSERT INTO Client..." in the same way...

• Health warning:– TAKE SPECIAL CARE WITH SPACES AND QUOTES

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Updating an Existing Row

• To update a row, first get it into the ResultSet:Statement stmt = con.createStatement();String code = "CR56";String sql = "SELECT * FROM Client" +" WHERE ClientNo ="+

" '" + code + "'" + ";";" '" + code + "'" + ";";ResultSet rs = stmt.executeQuery(sql);rs.absolute(1); // move to first \& only rowrs.updateDouble("MaxRent", 500.0);rs.updateString("PrefType", "House");rs.updateRow();rs.close();

• Here, ResultSet must contain the primary key ‐ why?

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Handling NULLs

• The JDBC API handles NULLs using a special method function: wasNull()– Have to "get" a field value, and then test for NULL ...String x = rs getString("City");String x = rs.getString( City );if (rs.wasNull()) x = "NULL";int i = rs.getInt("Rooms");if (rs.wasNull()) i = -1; // or whatever

• Your code can then test for special value later...

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Summary

• Programming model:

• Client (Java) sends SQL strings to server (DBMS)

• Server (DBMS) sends a ResultSet back to client...

• Programming features:

• JDBC is strongly typed: getString() getInt()• JDBC is strongly typed: getString(), getInt()...

• JDBC throws exceptions whenever there's a error

• Consider type of cursor: scrollable/updateable?

• ResultSet rows & columns count from ONE

• ResultSet cursor starts BEFORE the first row

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Documents

Java Databases Stuff