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8. OOPs

Question: 59
Click the Exhibit button.
11. class Payload {
12. private int weight;
13. public Payload(int wt) { weight = wt; }
13. public void setWeight(mt w) { weight = w; }
15. public String toString { return Integer.toString(weight); }
16. }
17.
18. public class TestPayload {
19. static void changePayload(Payload p) {
20. /* insert code here */
21. }
22.
23. public static void main(String[] args) {
24. Payload p = new Payload();
25. p.setWeight(1024);
26. changePayload(p);
27. System.out.println(”The value of p is “+ p);
28. }
29. }
Which statement, placed at line 20, causes the code to print “The
value of p is 420.”?
A. p.setWeight(420);
B. p.changePayload(420);
C. p = new Payload(420);
D. Payload.setWeight(420);
E. p = Payload.setWeight(420);
F. p = new Payload();
p.setWeight(420);
Answer: A

60. Which statement(s) are true? (Choose all that apply.)
A. Has-a relationships always rely on inheritance.
B. Has-a relationships always rely on instance variables. C. Has-a relationships always require at least two class types.
D. Has-a relationships always rely on polymorphism.
E. Has-a relationships are always tightly coupled.
Answer:
->  B is correct.
-> A and D describe other OO topics. C is incorrect because a class can have an instance of itself. E is incorrect because while has-a relationships can lead to tight coupling, it is by no means always the case.

61. Given:
class Clidders {
public final void flipper() { System.out.println("Clidder"); }
}
public class Clidlets extends Clidders {
public void flipper() {
System.out.println("Flip a Clidlet");
super.flipper();
}
public static void main(String [] args) {
new Clidlets().flipper();
}
}
What is the result?
A. Flip a Clidlet
B. Flip a Clidder
C. Flip a Clidder
Flip a Clidlet
D. Flip a Clidlet
Flip a Clidder
E. Compilation fails.
Answer:
->  E is correct. final methods cannot be overridden.
->A, B, C, and D are incorrect based on the above.

 

62. Given:
public abstract interface Frobnicate { public void twiddle(String s); }
Which is a correct class? (Choose all that apply.)
A. public abstract class Frob implements Frobnicate {
public abstract void twiddle(String s) { }
}
B. public abstract class Frob implements Frobnicate { }
C. public class Frob extends Frobnicate {
public void twiddle(Integer i) { }
}
D. public class Frob implements Frobnicate {
public void twiddle(Integer i) { }
}
E. public class Frob implements Frobnicate {
public void twiddle(String i) { }
public void twiddle(Integer s) { }
}

 

Answer:
->B is correct, an abstract class need not implement any or all of an interface’s methods. E is correct, the class implements the interface method and additionally overloads the twiddle() method.
->    A is incorrect because abstract methods have no body.
       C is incorrect because classes implement interfaces they don’t extend them.
       D is incorrect because overloading a method is not implementing it.

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