Ifi7107 lesson1- Programming languages

IFI7102 – Lesson 1

Introduction and contextualization

@ slides adapted from Isaías da Rosa sources

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Outline

Java programing language

Object-oriented concepts

Java IDEs

Eclipse working environment

Variables and Types

Strings

Variables and Assignment

Primitive Data Types

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Java programming language

• Dynamic Web applications– Servlets, JSP

• Native applications– Android and blackberry

• Java is not – Javascript– Native IOS

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Java is…

• A complied language– Has restrictive rules but is not difficult

• Similar languages– C, C + +, c#, Javascript, PHP

• Although…– You need to understand

• Rules – basic programming vocabulary

• The principles of object-oriented language

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First steps on Java

• Basic Structure– Object-oriented concepts

• Understand programming concepts like– What is a statement– What is a variable– What is a function– What is a condition

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Development Environments

• Applications that support Java development:

– Eclipse SE Development Kit (JDK)

• Runtime, compiler and other tools

– NetBeans

– BlueJ

• Though the details of these environments differ,

– the basic compilation and execution process is essentially the same

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Java Translation• Java is an

– interpreted language

– Is portable

• The Java compiler translates into

– Java bytecode

• We will use a Java virtual machine

– Eclipse

Java sourcecode Java

bytecode

Javacompiler

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Outline



Java IDEs


Variables and Types

Strings



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• What is an Object?– An object-oriented -> aims to -> model real-world

objects• examples of real-world objects: dog, desk, computer,

bicycle

– Characteristics of real-world object• have state and behaviour

– State = name, color, breed, hungry– Behaviour = barking, fetching, wagging tail

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A bicycle modeled as a object

StateVariables (fields)

behaviours functions (methods)

speed

Pedal cadence

gear

that allow to change the state

Function to change the gear (bicycle has 3 gears)

1. Reject values < 1 or > than 3

2. Verify what is the current gear

3. Change the gear

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What we know

• What are variables -> state – state of an object in real-world

• What are functions (methods) -> behaviours– Behaviour of that object in real world

• But…– Take the bicycle example

• 1 model/brand can have similar types of bicycle • How to represent in object-oriented terms?

– Using classes

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What Is a Class?

• A Class represent 1 object (bicycle) – or 1 or more objects (bicycles)

• Objects with similar characteristics of Object bicycle:– Same model, same company, same set of blueprints, same

components

InstanceOf

class of objects known as bicycles

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What Is a Inheritance?

• Represent 1 object (bicycle) – Which shares

• general and specific characteristics

– Object bicycle:• Shared characteristics

– class bicycles

• Specific characteristics – superclass – MountainBike and TandemBike

– How do you represent as object term?inherit

characteristics

class of objects known as bicyclesSuperclass of objects known as specific characteristic

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Instance

• An object and an instance in java language – are the same thing

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Identifier

• What is it?– Identifiers are the "words" in a program

• How can it be represented?– letters, digits, the underscore character ( _ ),

and the dollar sign– Not with a digit

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Outline



Java IDEs


Variables and Types

Strings



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DEMO

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Eclipse IDE

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https://eclipse.org/downloads/

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Java Application

• Consists – Of many classes (.java) – command line runtime – The packager (jar) – aggregates the many

classes– The javadoc – the documentation builder– The command line compiler - javac

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First step

• Set up the workspace• Create 1 application

– Create a project– SRC AND BIN folders

• Every Java App Is Build Inside A Class• Create a new class

– System.out.println(“Hello World”)– Compile or run java application

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public class HelloWorld {

public static void main(String[] args) {

System.out.println("Hello world" );

}

}

Java Program Structure

Hello World!

Class declaration

File name: HelloWorld.java Java is Case sensitive Language

=

Main method

Executable code

Compile resultsFile sources

HelloWorld.class

HelloWorld.java

Bytecode file

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Java syntax

The method can be called anywhere

A method contains1 program statements

public class MyProgram{

}

// comments about the class

public static void main (String[] args)

{

}

// Main method declaration

method headermethod bodyDon’t have to create a instance of a class

Do not return anything from the class

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New public class called MyProgram

class body

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The println Method

• The println method prints a character string

• The System.out object represents a destination (the monitor screen) to which we can send output

System.out.println ("Whatever you are, be a good one.");

information provided(arguments)

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Resulting files

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Sum…

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Basic Program Development

errors?

errors?

Edit andsave program

Compile program

Execute program andevaluate results

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Java Translation

Java sourcecode

Machinecode

Javabytecode

Bytecodeinterpreter

Bytecodecompiler

Javacompiler

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A class in java

• Can be inside of a package– That is a group of classes with common characteristics

• Java includes a library of classes – Each class -> has a property

• Most common used is– Java.lang (Packages)– Search on google for java 6 api docs

• Java program is made of an aggregation of – 1 or + classes

• We are going to use – The System class -> belongs to Java.lang– The out variable -> PrintStream class -> System class – println and print method2015

http://docs.oracle.com/javase/7/docs/api/

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Errors

• A program can have three types of errors1) Compile-time errors

• The compiler will find syntax errors and other basic problems • If compile-time errors exist, an executable version of the

program is not created

2) Run-time errors • A problem can occur during program execution, such as

– trying to divide by zero, which causes a program to terminate abnormally

3) Logical errors • A program may run, but produce incorrect results, perhaps

using an incorrect formula

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Comments

• Comments should always be included

– To explain the purpose of the program; and

– Describe processing steps.

• They do not affect how a program works

• Java comments can take three forms:

// this comment runs to the end of the line

/* this comment runs to the terminating symbol, even across line breaks */

/** this is a javadoc comment */

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Java is Case sensitive

• Java is case sensitive:– Total, total, and TOTAL are different

identifiers

• Rules on how to…– use different case styles for different types of

identifiers• Class names start with upper case – MyProgram• Variables with lower case - value

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Reserved words

• Identifiers with a predefined meaning in the language– println

• A reserved word cannot be used in any other way

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Reserved Words

• The Java reserved words:abstractassertbooleanbreakbytecasecatchcharclassconstcontinuedefaultdodouble

elseenumextendsfalsefinalfinallyfloatforgotoifimplementsimportinstanceofint

interfacelongnativenewnullpackageprivateprotectedpublicreturnshortstaticstrictfpsuper

switchsynchronizedthisthrowthrowstransienttruetryvoidvolatilewhile

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EXERCISE 1

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Quick CheckWhich of the following are valid Java identifiers?

grade

quizGrade

NetworkConnection

frame2

3rdTestScore

MAXIMUM

MIN_CAPACITY

student#

Shelves1&2

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Quick CheckWhich of the following are valid Java identifiers?

grade

quizGrade

NetworkConnection

frame2

3rdTestScore

MAXIMUM

MIN_CAPACITY

student#

Shelves1&2

Valid

Valid

Valid

Valid

Invalid – cannot begin with a digit

Valid

Valid

Invalid – cannot contain the '#' character

Invalid – cannot contain the '&' character

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Outline



Java IDEs


Variables and Types

Strings



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Character Strings

• A string literal is represented by putting double quotes around the text

• Examples:

"This is a string literal.""123 Main Street""X”

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EXERCISE 2

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//********************************************************************// Countdown.java Author: Lewis/Loftus//// Demonstrates the difference between print and println.//********************************************************************

public class Countdown{ //----------------------------------------------------------------- // Prints two lines of output representing a rocket countdown. //----------------------------------------------------------------- public static void main (String[] args) { System.out.print ("Three... "); System.out.print ("Two... "); System.out.print ("One... "); System.out.print ("Zero... "); System.out.println ("Liftoff!"); // appears on first output line System.out.println ("Houston, we have a problem."); }}

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//********************************************************************// Countdown.java Author: Lewis/Loftus//// Demonstrates the difference between print and println.//********************************************************************

public class Countdown{ //----------------------------------------------------------------- // Prints two lines of output representing a rocket countdown. //----------------------------------------------------------------- public static void main (String[] args) { System.out.print ("Three... "); System.out.print ("Two... "); System.out.print ("One... "); System.out.print ("Zero... "); System.out.println ("Liftoff!"); // appears on first output line System.out.println ("Houston, we have a problem."); }}

Output

Three... Two... One... Zero... Liftoff!Houston, we have a problem.

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String Concatenation

• The string concatenation operator (+) is used to append one string to the end of another

"Peanut butter " + "and jelly"

• It can also be used to append a number to a string

• A string literal cannot be broken across two lines in a program

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EXERCISE 3

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//********************************************************************// Facts.java Author: Lewis/Loftus//// Demonstrates the use of the string concatenation operator and the// automatic conversion of an integer to a string.//********************************************************************

public class Facts{ //----------------------------------------------------------------- // Prints various facts. //----------------------------------------------------------------- public static void main (String[] args) { // Strings can be concatenated into one long string System.out.println ("We present the following facts for your " + "extracurricular edification:");

System.out.println ();

// A string can contain numeric digits System.out.println ("Letters in the Hawaiian alphabet: 12");

continue

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continue

// A numeric value can be concatenated to a string System.out.println ("Dialing code for Antarctica: " + 672);

System.out.println ("Year in which Leonardo da Vinci invented " + "the parachute: " + 1515);

System.out.println ("Speed of ketchup: " + 40 + " km per year"); }}

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continue

// A numeric value can be concatenated to a string System.out.println ("Dialing code for Antarctica: " + 672);

System.out.println ("Year in which Leonardo da Vinci invented " + "the parachute: " + 1515);

System.out.println ("Speed of ketchup: " + 40 + " km per year"); }}

OutputWe present the following facts for your extracurricular edification:

Letters in the Hawaiian alphabet: 12Dialing code for Antarctica: 672Year in which Leonardo da Vinci invented the parachute: 1515Speed of ketchup: 40 km per year

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String Concatenation

• The + operator is also used for arithmetic addition

– The function that it performs depends on the type of the information on which it operates

• If both operands are strings, or if one is a string and one is a number,

– it performs string concatenation

• If both operands are numeric, it adds them

• The + operator is evaluated left to right, but parentheses can be used to force the order

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EXERCISE 4

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//********************************************************************// Addition.java Author: Lewis/Loftus//// Demonstrates the difference between the addition and string// concatenation operators.//********************************************************************

public class Addition{ //----------------------------------------------------------------- // Concatenates and adds two numbers and prints the results. //----------------------------------------------------------------- public static void main (String[] args) { System.out.println ("24 and 45 concatenated: " + 24 + 45);

System.out.println ("24 and 45 added: " + (24 + 45)); }}

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//********************************************************************// Addition.java Author: Lewis/Loftus//// Demonstrates the difference between the addition and string// concatenation operators.//********************************************************************

public class Addition{ //----------------------------------------------------------------- // Concatenates and adds two numbers and prints the results. //----------------------------------------------------------------- public static void main (String[] args) { System.out.println ("24 and 45 concatenated: " + 24 + 45);

System.out.println ("24 and 45 added: " + (24 + 45)); }}

Output

24 and 45 concatenated: 244524 and 45 added: 69

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EXERCISE 5

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Quick Check

• What output is produced by the following?

System.out.println ("X: " + 25);System.out.println ("Y: " + (15 + 50));System.out.println ("Z: " + 300 + 50);

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Quick Check

X: 25Y: 65Z: 30050


System.out.println ("X: " + 25);System.out.println ("Y: " + (15 + 50));System.out.println ("Z: " + 300 + 50);

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EXERCISE 6

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Quick Check


System.out.println ("I said "Hello" to you.");

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Quick Check

An escape sequence begins with a backslash character (\)

System.out.println ("I said \"Hello\" to you.");

• The compiler becomes confuse– would interpret the second quote as the end

of the string

System.out.println ("I said "Hello" to you.");

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EXERCISE 7

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Escape Sequences

• Some Java escape sequences:

Escape Sequence

\b\t\n\r\"\'\\

Meaning

backspacetabnewlinecarriage returndouble quotesingle quotebackslash

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//********************************************************************// Roses.java Author: Lewis/Loftus//// Demonstrates the use of escape sequences.//********************************************************************

public class Roses{ //----------------------------------------------------------------- // Prints a poem (of sorts) on multiple lines. //----------------------------------------------------------------- public static void main (String[] args) { System.out.println ("Roses are red,” + “Violets are blue," + "Sugar is sweet,\n\tBut I have \"commitment issues\",\n\t" + "So I'd rather just be friends\n\tAt this point in our " + "relationship."); }}

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//********************************************************************// Roses.java Author: Lewis/Loftus//// Demonstrates the use of escape sequences.//********************************************************************

public class Roses{ //----------------------------------------------------------------- // Prints a poem (of sorts) on multiple lines. //----------------------------------------------------------------- public static void main (String[] args) { System.out.println ("Roses are red,\n\tViolets are blue,\n" + "Sugar is sweet,\n\tBut I have \"commitment issues\",\n\t" + "So I'd rather just be friends\n\tAt this point in our " + "relationship."); }}

Output

Roses are red, Violets are blue,

Sugar is sweet,But I have "commitment issues",So I'd rather just be friendsAt this point in our relationship.

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EXERCISE 8

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Quick Check

• Write a single println statement that produces the following output:

"Thank you all for coming to my hometonight," he said mysteriously.

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• Write a single println statement that produces the following output:

Quick Check

"Thank you all for coming to my hometonight," he said mysteriously.

System.out.println ("\"Thank you all for " + "coming to my home\ntonight,\" he said " + "mysteriously.");

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Outline



Java IDEs


Variables and Types

Strings



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EXERCISE 9

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Variables

• A variable is a name for a

– location in memory that holds a value

• When you declare a variable (variable declaration)

– you need to specify

int total;

int count, temp, result;

Multiple variables can be created in one declaration

data type variable name

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Variable Initialization

• You can add a initial value to your variable

int sum = 0;int base = 32, max = 149;

data type variable namevariable value = 0

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EXERCISE 10

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//********************************************************************// PianoKeys.java Author: Lewis/Loftus//// Demonstrates the declaration, initialization, and use of an// integer variable.//********************************************************************

public class PianoKeys{ //----------------------------------------------------------------- // Prints the number of keys on a piano. //----------------------------------------------------------------- public static void main (String[] args) { int keys = 88; System.out.println ("A piano has " + keys + " keys."); }}

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//********************************************************************// PianoKeys.java Author: Lewis/Loftus//// Demonstrates the declaration, initialization, and use of an// integer variable.//********************************************************************

public class PianoKeys{ //----------------------------------------------------------------- // Prints the number of keys on a piano. //----------------------------------------------------------------- public static void main (String[] args) { int keys = 88; System.out.println ("A piano has " + keys + " keys."); }}

Output

A piano has 88 keys.

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Assignment

• An assignment statement

– Changes the value of a variable

• What happens?• The value that was in total is overwritten

• You need to assign a value to a variable = variable's declared type

• Int , byte, short, long, float, double, boolean, char

• See more about primitive Data types

total = 55;

Assignment operator

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EXERCISE 11

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//********************************************************************// Geometry.java Author: Lewis/Loftus//// Demonstrates the use of an assignment statement to change the// value stored in a variable.//********************************************************************

public class Geometry{ //----------------------------------------------------------------- // Prints the number of sides of several geometric shapes. //----------------------------------------------------------------- public static void main (String[] args) { int sides = 7; // declaration with initialization System.out.println ("A heptagon has " + sides + " sides.");

sides = 10; // assignment statement System.out.println ("A decagon has " + sides + " sides.");

sides = 12; System.out.println ("A dodecagon has " + sides + " sides."); }}

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//********************************************************************// Geometry.java Author: Lewis/Loftus//// Demonstrates the use of an assignment statement to change the// value stored in a variable.//********************************************************************

public class Geometry{ //----------------------------------------------------------------- // Prints the number of sides of several geometric shapes. //----------------------------------------------------------------- public static void main (String[] args) { int sides = 7; // declaration with initialization System.out.println ("A heptagon has " + sides + " sides.");

sides = 10; // assignment statement System.out.println ("A decagon has " + sides + " sides.");

sides = 12; System.out.println ("A dodecagon has " + sides + " sides."); }}

Output

A heptagon has 7 sides.A decagon has 10 sides.a dodecagon has 12 sides.

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Constants

• A constant is an identifier

– that is similar to a variable except that it holds the same value during its entire existence

• As the name implies, it is constant, not variable

• The compiler will issue an error if you try to change the value of a constant

• In Java, we use the final modifier to declare a constant

final int MIN_HEIGHT = 69;

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Constants

• Constants are useful for three important reasons

1) First, they give meaning to otherwise unclear literal values

• Example: MIN_HEIGHT means more than the literal 69

2) Second, they facilitate program maintenance

• If a constant is used in multiple places, its value need only be set in one place

3) Third, they formally establish that a value should not change,

• Avoiding inadvertent errors by other programmers

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Outline



Java IDEs


Variables and Types

Strings



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Primitive Data

• There are eight primitive data types in Java

• Four of them represent integers:– byte, short, int, long

• Two of them represent floating point numbers:– float, double

• One of them represents characters:– char

• And one of them represents boolean values:– boolean

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Most common Types• int

– integer (most common. no decimal)• long

– holds a really big integer• float

– accurate up to 7 decimal places • double

– accurate up to 15 decimal places I do believe (at work and don't have a book)• boolean

– false or true (also 1 = true, 0 = false)• string

– anything from numbers to letters to whole sentences. It will take the input literately.• char

– character, such as f or 6 or \

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Numeric Primitive Data

• The difference between the numeric primitive types is their size and the values they can store:

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Type

byteshortintlong

floatdouble

Storage

8 bits16 bits32 bits64 bits

32 bits64 bits

Min Value

-128-32,768-2,147,483,648< -9 x 1018

- 3.4 x 1038 3.4 x 1038

- 1.7 x 10308 1.7 x 10308

Max Value

12732,7672,147,483,647> 9 x 1018

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Characters

• A char variable stores a single character

• Character literals are delimited by single quotes:

'a' 'X' '7' '$' ',' '\n'

• Example declarations:

char topGrade = 'A';char terminator = ';', separator = ' ';

• Note the difference between

– a primitive character variable, which holds only one character, and

– a String object, which can hold multiple characters

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Character Sets

• A character set is an ordered list of characters, with each character corresponding to a unique number

• A char variable in Java can store any character from the Unicode character set

• The Unicode character set uses sixteen bits per character, allowing for 65,536 unique characters

• It is an international character set, containing symbols and characters from many world languages

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Characters

• The ASCII character set is older and smaller than Unicode, but is still quite popular

• The ASCII characters are a subset of the Unicode character set, including:

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uppercase letterslowercase letterspunctuationdigitsspecial symbolscontrol characters

A, B, C, …a, b, c, …period, semi-colon, …0, 1, 2, …&, |, \, …carriage return, tab, ...

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Boolean

• A boolean value represents a true or false condition

• The reserved words true and false are the only valid values for a boolean type

boolean done = false;

• A boolean variable can also be used to represent any two states, such as a light bulb being on or off

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Education

Ifi7107 lesson1- Programming languages