CSE 1020:Inheritance Mark Shtern

Course evaluations Lecture: Tuesday, July 12 Lab: Tuesday, July 12 Both will take place at the beginning of the lecture / lab

Summary Aggregation Collection Composition Traversing

UML

Definition C extends P: Every fields and public method present in P is also present in C Extend is inheritance relation between the child and parent C is a P C is specialization of P and P is generalization of C

UML diagram

Inheritance Inheritance chain Inheritance hierarchy Descendant Java does not allow multiple- inheritance

Subclass API The constructor section The method section Overriding methods Override vs Overload The field section Shadow Field

Example 903 Examine API of the reward card subclass and its supper class, and identify the methods that were Overridden Added by subclass Provide a rational to justify why these methods were overridden or added

The substitutability Principle It says: When parent is expected, a child is accepted output.println(“Enter C or P”); char choice = input.nextChar(); P x; If (choice ==‘P’) { x = new P(); } else { x = new C(); }

Example 904 Write a fragment that asks the user whether an ordinary or a reward card is wanted, then create the appropriate card with card number 9 and cardholder name “Adam” CreditCard card; If (type.equals(“O”)) { card = new CreditCard(9,”Adam”); } else { card = new RewardCard(9,”Adam”); }

Early and Late Binding The compiler performs early binding as before Assuming no errors, it culminates in a target VM performs late binding Determine the class of the object If reference null, then a “Null Point Exception” is thrown Searches for method with matching signature and binds with it

What is expected output CreditCard card1 = new RewardCard(9, “Adam”); CreditCard card2 = new RewardCard(9, “Adam”); card1.charge(500); card1.pay(500); output.println(card1.isSimilar(card2));

Polymorphism CreditCard card; .... Card.charge(500.0); Polymorphic is capable of having multiple forms Polymorphism refers to the ability of the same entity to have multiple forms instanceof

Predict output of the following code CreditCard card1 = new RewardCard(9, “Adam”); CreditCard card2 = new RewardCard(9, “Adam”); card1.charge(500); card1.pay(100); output.println(card1.isSimilar(card2)); output.println(card1.isSimilar((RewardCard)card2)); output.println((RewardCard)card1.isSimilar(card2)); output.println((RewardCard)card1.isSimilar((RewardCard)card2));

Abstract Class Abstract class does not encapsulate an actual object

Abstract Class API public abstract class Vehicle Factory Method Vehicle myCar = Vehicle.createCar(); Subclass constructor Vehicle myCar = new Car();

Example 908 Create an instance of the type Calendar

Interface Interface retains only Constants Contracts of the shared methods

Interface A class contains implementation of all interface methods is said to implement interface Implementation is-a relation A class can implement as many interfaces as needed

Object Class Boolean equals(Object other) String toString() Class getClass()

Generic Generic or Parameterized Type The generic idea allows an implementer to write a component that can handle only one type T but without specifying T Bar<CreaditCard> bag = new Bag<CreaditCard>();

Summary Inheritance, Polymorphism and Substitutability, Binding Interfaces, Abstract class Generic

Exercise 9.4 (modified) Determine the API of class Bee in this UML diagram

Exercise 905678 Based on the inheritance chain determine whether the following fragments have Compiler-error Run-time error Justify the cast in

Exercise 920 The following fragment seeks to invoke toString method of the Object class in order to determine the memory address of a Fraction instance Object tmp = new Fraction(); output.println(tmp.toString()); output.println((Object)tmp.toString()); Predict and Explain the output

Exercise 922 Consider the following fragment Fraction x = new Money(2.25); Money y = new Money(5.27); output.println(x.resembles(y)); output.println(((MixedNumber)x).resembles(y)); output.println(((Money)x).resembles(y)); Predict output

Same as previous (Exercise 921) Fraction x = new Money(2.25); Fraction xFr = new Fraction(225, 100); Fraction yFr = new Fraction(527, 100); output.println(xFr.resembles(yFr)); MixedNumber xMi = new MixedNumber(1, 2, 25, 100); MixedNumber yMi = new MixedNumber(1, 5, 27, 100); output.println(xMi.resembles(yMi)); Money xMo = new Money(2.25); Money yMo = new Money(5.27); output.println(xMo.resembles(yMo));

Exercise 9.16 Write a program that generates statistics about the return type of the getRandom method of the MixedNumber class Invoke 100 times and output the number of times a Fraction or a MixedNumber was returned Use instanceof

Exercise 9.17 Write a program that generates statistics about the return type of the getRandom method of the MixedNumber class Invoke 100 times and output the number of times a Fraction or a MixedNumber was returned Use getClass