Advanced Objects(Dependencies and Documentation)

Java Class Concept

Encapsulation◦ Blackbox concept

Data and method(s)Hidden details

Interface Effect(s)

methods called

class

Relationship Symbol Line Style

Arrow Tip

Inheritance-is-a

                                         

Solid Triangle

Interface Implementation

                                    

      Dotted Triangle

Aggregation-has-a

                                          

Solid Diamond

Dependency

                                         

Dotted Open

UML Relationship Symbols

Aggregation is a stronger form of dependency-see page 467

                                                                                                                            

• Place multiplicity notations near the ends of an association/• dependency.

Multiplicity (Cardinality)

GJY

1..*

has-a relationship

Establishes has-a relationship/association between classes BankAccount One can navigate from one class to another instantiation in Java – (note NOT inheritance)

package bankaccount;public class BankAccount {

private double balance;public BankAccount () { balance=0; }public void deposit (double amount) { balance=balance+amount; }public void withdraw (double amount){ balance=balance - amount; }public double getBalance () {

return balance;}

}

package bankaccount;public class Bank {

public static void main(String[] args) { BankAccount harrysChecking = new BankAccount(); harrysChecking.deposit(2000.00); harrysChecking.withdraw(500.00); System.out.println(harrysChecking.getBalance()); }}

Review BankAccount

Lab: Part 1

1. Add the interest method to your BankAccount Class2. Add an account with your name3. Call interest for Harry and pass 5% or .054. Call the interest method for your account and pass the parameter as .085. Revise VISIO drawing accordingly

Chapter 8, pp 304-307 pre & post conditions Section 8.5

Documentation Comments

Documentation included in form of comments◦Prior to a class◦Prior to a method◦Begins with “/**” and ends with “*/”

Internal Method comments discouraged

• Objective:

Tells other programmers how to use the method!

• precondition documentation• postcondition documentation

Precondition: describes the state of relevant identifiers prior to the function's execution.

• Includes a reference to what variables are passed to the function. • Postcondition: describes the state after the function is executed:

• the state of attributes after execution• the return value if any.

Do NOT:1) Repeat code description! (code is hidden and user/programmer on needs to

know what to expect and what must be supplies)

2) Describe how code works3) Do not use attribute names unless meaningful

• Precondition Publish preconditions so the caller won't call methods with

bad parameters

Preconditions

• Method should let user know if condition is violated.

• Caution: Text might imply otherwise

• Condition that is true after a method has completed

• The return value is computed correctly • The object is in a certain state after the method call is completed

• Don't document trivial postconditions that repeat the @return clause

Postconditions

/** * precondition: Balance is available for an account * @param amount >=0 * postcondition:The account balance is adjusted to reflect * the deposit. */public void deposit (double amount){

System.out.println(amount);balance = balance + amount;

}

Lab: Part 2

Enhance the BankAccount Class Add preconditions for all methods Add parameters to documentation as

necessary Add postconditions where applicable Post Complete labs to DropBoxes

located in September 19th ANGEL Lesson Tab

Chapter 10

Inheritance

Inheritance : derive a new class from an existing one

Parent class, or superclass, or base class.

Thechild class or subclass.

Component hierarchy:

Inheritance (generalization)

is-a relationship between superclass and a subclass or base class

Inheritance

Deposit

BankForm parent

Is-a component of

child

Business

KMart Macys

ServiceBusiness

Kinkos

RetailBusiness

is-a

Deriving SubclassesJAVA Example 1: class RetailBusiness extends Business

Example 2:class CheckingAccount extends BankAccount{

<class contents>}

SavingsAccount object inherits the balance instance field from BankAccount, and gains one additional instance field: interestRate:

Layout of a Subclass Object

public class BankAccount{ private double balance;/** * PostCondition: A bank account with a zero balance.*/ public BankAccount() { balance = 0; } /** @param initialBalance the initial balance PostCondition: A bank account with a given balance is constructed. */ public BankAccount(double initialBalance) { balance = initialBalance; }

Continued Next Page

/** * PreCondition: a balance exists @param amount the amount to deposit PostCondition: Money is deposited into the bank account. */ public void deposit(double amount) { double newBalance = balance + amount; balance = newBalance; } /** * Precondition: A balance exists @param amount the amount to withdraw PostCondition: Money is withdrawn from the bank account. */ public void withdraw(double amount) { double newBalance = balance - amount; balance = newBalance; } /** PostCondition: Current balance of the bank account exists. @return the current balance */ public double getBalance() { return balance; }}

BankAccount Class Continued

package infsy535bankacctwithinheritance;public class SavingsAccount extends BankAccount { private double interestRate; /** @param rate the interest rate PostCondition: A bank account with a given interest rate. */ public SavingsAccount(double rate) { interestRate = rate; } /** PostCondition: Added the earned interest to the account balance. */ public void addInterest() { double interest = getBalance() * interestRate / 100; deposit(interest); } }

Savings Account