Example of Aggregation 1) aggregation - the class contains other structure(s) 2) specialization - the new class is a special case of the data structure public class PersonalInfo { private String firstName, lastName; private char midInitial; private Address street;... } PersonalInfo StringAddress 2 Two ways to use a data structure to implement a class The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

Inheritance When one class inherits another class, the new class becomes a specialized version of the original. Java Syntax public class childClass extends parentClass {... } UML (class diagram) Notation parentClass childClass The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

Example of Specialization Consider the relationships among classes for the following: TimePiece GrandfatherClock DigitalWatch Note that GrandfatherClock is a TimePiece DigitalWatch is a TimePiece TimePiece GrandfatherClockDigitalWatch The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

Review of Inheritance How do you express inheritance in Java? parentClass childClass What is meant by overriding a method? (Note that variables can’t be overridden.) What does a child class inherit from its parent class? Can the child class declare additional variables & methods? Does the child class inherit constructor methods? What is the notation for calling a parent class constructor? Parent class constructor calls are only permitted in one location. Where? How does a child class refer to the parent class version of an overridden method? When is the following expression true? a instanceof b Are private members from a parent class accessible within a child class?... public members?... protected members? The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

public class BasicCheckbook { protected int balance; // in cents /* post: balance == bd*100 + bc */ public BasicCheckbook(int bd, int bc) { balance = bd*100 + bc; } /* post: balance == + dd*100 + dc */ public void deposit(int dd, int dc) { balance = balance + dd*100 + dc; } /* post: balance == - (wd*100 + wc)*/ public void withdraw(int wd, int wc) { balance = balance - (wd*100 + wc); } /* post: result == balance */ public int balanceInCents() { return balance; } BasicCheckbook # balance : int «constructor» + BasicCheckbook( int, int) «update» + deposit( int, int) + withdraw( int, int) «query» + balanceInCents() : int protected public private is “-” The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

Including a toString method (returns the balance as a String) The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

public class CheckbookWithStrBalance extends BasicCheckbook { public CheckbookWithStrBalance(int bd, int bc) { super(bd, bc); } public String toString() { String dollarStr, centStr; int cents; dollarStr = "" + (balance / 100); cents = balance % 100; if (cents < 10) { centStr = "0" + cents; } else { centStr = "" + cents; } return "$" + dollarStr + "." + centStr; } BasicCheckbook # balance : int «constructor» + BasicCheckbook( int, int) «update» + deposit( int, int) + withdraw( int, int) «query» + int balanceInCents() CheckbookWithStrBalance «constructor» + CheckbookWithStr...( int, int) «query» + String toString() The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

Maintain total amounts for deposits and withdrawls The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

public class CheckbookWithTotals extends CheckbookWithStrBalance { protected int depositTot, withdrawTot; public CheckbookWithTotals(int bd, int bc) { super(bd, bc); depositTot = 0; withdrawTot = 0; } public void deposit(int dd, int dc) { super.deposit(dd, dc); depositTot = depositTot + dd*100 + dc; } public void withdraw(int wd, int wc) { super.withdraw(wd, wc); withdrawTot = withdrawTot - (wd*100 + wc); } public int deposits() { return depositTot; } public int withdraws() { return withdrawTot; } BasicCheckbook # int balance «constructor» + BasicCheckbook( int, int) «update» + deposit( int, int) + withdraw( int, int) «query» + int balanceInCents() CheckbookWithStrBalance «constructor» + CheckbookWith...( int, int) «query» + String toString() CheckbookWithTotals # int depositTot # int withdrawTot «constructor» + CheckbookWithTotals( int, int) «update» + deposit( int, int) + withdraw( int, int) «query» + int deposits() + int withdraws()

Permit overdraft (negative balance) (charge $10 for each transaction in the red) The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.

public class CheckbookWithRedInk extends CheckbookWithTotals { public CheckbookWithRedInk(int bd, int bc) { super(bd, bc); } public void deposit(int dd, int dc) { super.deposit(dd, dc); if (dd*100+dc < 0 && balance < 0) { System.out.println("$10 surcharge"); balance = balance ; } public void withdraw(int wd, int wc) { super.withdraw(wd.wc); if (wd*100+wc > 0 && balance < 0) { System.out.println("$10 surcharge"); balance = balance ; } public String toString() { String str; if (balance >= 0) { str = super.toString(); } else { balance = -balance; str = "(" + super.toString() + ")"; balance = -balance; } return str; } BasicCheckbook # int balance «constructor» + BasicCheckbook( int, int) «update» + deposit( int, int) + withdraw( int, int) «query» + int balanceInCents() CheckbookWithStrBalance «constructor» + CheckbookWith...( int, int) «query» + String toString() CheckbookWithTotals # int depositTot # int withdrawTot «constructor» + CheckbookWithTotals( int, int) «update» + deposit( int, int) + withdraw( int, int) «query» + int deposits() + int withdraws()

public class Director { private CheckbookWithRedInk checkbook; public Director() { checkbook = new CheckbookWithRedInk( 100, 0 ); checkbook.deposit( 20, 0 ); checkbook.withdraw( 125, 99 ); System.out.println("Final Balance: " + checkbook.toString()); } CheckbookWithRedInk # int balance # int depositTot # int withdrawTot «constructor» + CheckbookWithRedInk( int, int) «update» + deposit( int, int) + withdraw( int, int) «query» + int balanceInCents() + String toString() + int deposits() + int withdraws() A flattened version of the class A client The Object of Data Abstraction and Structure, David D. Riley © Addison Wesley pub.