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8. OOPs

Q: 24 Given:
10. abstract class A {
11. abstract void a1();
12. void a2() { }
13. }
14. class B extends A {
15. void a1() { }
16. void a2() { }
17. }
18. class C extends B { void c1() { } }
and:
A x = new B(); C y = new C(); A z = new C();
What are four valid examples of polymorphic method calls? (Choose four.)
A. x.a2();
B. z.a2();
C. z.c1();
D. z.a1();
E. y.c1();
F. x.a1();
Answer: A, B, D, F

Q: 25 Click the Exhibit button.

What is the result?

A. Value is: 8
B. Compilation fails.
C. Value is: 12
D. Value is: -12
E. The code runs with no output.
F. An exception is thrown at runtime.
Answer: A

Q: 26 Given:
20. public class CreditCard {
21.
22. private String cardID;
23. private Integer limit;
24. public String ownerName;
25.
26. public void setCardInformation(String cardID,
27. String ownerName,
28. Integer limit) {
29. this.cardID = cardID;
30. this.ownerName = ownerName;
31. this.limit = limit;
32. }
33. }
Which statement is true?
A. The class is fully encapsulated.
B. The code demonstrates polymorphism.
C. The ownerName variable breaks encapsulation.
D. The cardID and limit variables break polymorphism.
E. The setCardInformation method breaks encapsulation.
Answer: C

Q: 27Given:
11. class Animal { public String noise() { return "peep"; } }
12. class Dog extends Animal {
13. public String noise() { return "bark"; }
14. }

15. class Cat extends Animal {
16. public String noise() { return "meow"; }
17. }
...
30. Animal animal = new Dog();
31. Cat cat = (Cat)animal;
32. System.out.println(cat.noise());
What is the result?
A. peep
B. bark
C. meow
D. Compilation fails.
E. An exception is thrown at runtime.
Answer: E
Q: 28 Click the Task button.

Solution:
Dog                              is-a               Animal
Forest              has-a             Tree
Rectangle         has-a             Side
JavaBook          is-a             ProgrammingBook

Q: 29 Which three statements are true? (Choose three.)

A. A final method in class X can be abstract if and only if X is abstract.
B. A protected method in class X can be overridden by any subclass of X.
C. A private static method can be called only within other static methods in class X.
D. A non-static public final method in class X can be overridden in any subclass of X.
E. A public static method in class X can be called by a subclass of X without explicitly referencing the class X.
F. A method with the same signature as a private final method in class X can be implemented in a subclass of X.

G. A protected method in class X can be overridden by a subclass of A only if the subclass is in the same
package as X.
Answer: B, E, F
Q: 30 Which four statements are true? (Choose four.)

A. Has-a relationships should never be encapsulated.
B. Has-a relationships should be implemented using inheritance.
C. Has-a relationships can be implemented using instance variables.
D. Is-a relationships can be implemented using the extends keyword.

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