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8. OOPs

67. Given:
1. class Zing {
2. protected Hmpf h;
3. }
4. class Woop extends Zing { }
5. class Hmpf { }
Which is true? (Choose all that apply.)
A. Woop is-a Hmpf and has-a Zing.
B. Zing is-a Woop and has-a Hmpf.
C. Hmpf has-a Woop and Woop is-a Zing.
D. Woop has-a Hmpf and Woop is-a Zing.
E. Zing has-a Hmpf and Zing is-a Woop.

Answer:
->  D is correct, Woop inherits a Hmpf from Zing.
->  A, B, C, and E are incorrect based on the preceding.

68. Given:
1. class Programmer {
2. Programmer debug() { return this; }
3. }
4. class SCJP extends Programmer {
5. // insert code here
6. }
Which, inserted at line 5, will compile? (Choose all that apply.)
A. Programmer debug() { return this; }
B. SCJP debug() { return this; }
C. Object debug() { return this; }
D. int debug() { return 1; }
E. int debug(int x) { return 1; }
F. Object debug(int x) { return this; }
Answer:
->  A, B, E, and F are correct. A and B are examples of overriding, specifically, B is an
example of overriding using a covariant return. E and F are examples of overloading.
->  C and D are incorrect. They are illegal overrides because their return types are
incompatible. They are illegal overloads because their arguments did not change.

69. Given:
class Uber {
static int y = 2;
Uber(int x) { this(); y = y * 2; }
Uber() { y++; }
}
class Minor extends Uber {
Minor() { super(y); y = y + 3; }
public static void main(String [] args) {
new Minor();
System.out.println(y);
} }
What is the result?
A. 6                                B. 7
C. 8                                D. 9
E. Compilation fails.      F. An exception is thrown.
Answer:
-> D is correct. Minor’s constructor makes an explicit call to Uber’s 1-arg constructor,
which makes an explicit (this) call to Uber’s no-arg constructor, which increments y,
then returns to the 1-arg constructor, which multiples y * 2, and then returns to Minor’s
constructor, which adds 3 to y.
->  A, B, C, E, and F are incorrect based on the preceding.

70. Which statement(s) are true? (Choose all that apply.)

A. Cohesion is the OO principle most closely associated with hiding implementation details.
B. Cohesion is the OO principle most closely associated with making sure that classes know
about other classes only through their APIs.
C. Cohesion is the OO principle most closely associated with making sure that a class is
designed with a single, well-focused purpose.
D. Cohesion is the OO principle most closely associated with allowing a single object to be seen as having many types.
Answer:
->  Answer C is correct.
->  A refers to encapsulation, B refers to coupling, and D refers to polymorphism.

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