SCJP題庫第066題

5. class Thingy{ Meter m = new Meter(); }

6. class Component {void go() { System.out.print("c");}}

7. class Meter extends Component {void go() { System.out.print("m"); }}

8.

9. class DeluxeThingy extends Thingy {

10.   public static void main(String[] args) {

11.     DeluxeThingy dt = new DeluxeThingy();

12.     dt.m.go();

13.     Thingy t = new DeluxeThingy();

14.     t.m.go();

15.   }

16. }

Which two are true? (Choose two.)

 

 

A. The output is mm.

B. The output is mc.

C. Component is-a Meter.

D. Component has-a Meter.

E. DeluxeThingy is-a Component.

F. DeluxeThingy has-a Component.

 

Ans: A F

 

解說:

Meter繼承Component

DeluxeThingy 繼承Thingy ，Thingy 中有一個Meter物件(也是Component物件)，滿足F

因多形原則，m物件屬於Meter，因此二個go方法皆為Meter的go，印出m