1. CSE 1020:Inheritance
Mark Shtern

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

3. Summary
Aggregation
Collection
Composition
Traversing

4. UML

5. 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

6. UML diagram

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

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

10. 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

11. 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(); }

12. 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”); }

13. 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

14. 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));

15. 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

16. 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));

17. Abstract Class
Abstract class does not encapsulate an actual object

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

19. Example 908
Create an instance of the type Calendar

20. Interface Interface retains only Constants
Contracts of the shared methods

21. 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

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

23. 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>();

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

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

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

27. 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

28. 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

29. 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));

30. 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

31. 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