SCJP題庫第063題

11. class ClassA{}

12. class ClassB extends ClassA{}

13. class ClassC extends ClassA{}

and:

21. ClassA p0 = new ClassA();

22. ClassB p1 = new ClassB();

23. ClassC p2 = new ClassC();

24. ClassA p3 = new ClassB();

25. ClassA p4 = new ClassC();

Which three are valid? (Choose three.)

 

 

A. p0 = p1;

B. p1 = p2,

C. p2 = p4;

D. p2 = (ClassC)p1;

E. p1 = (ClassB)p3;

F. p2 = (ClassC)p4;

 

Ans: A E F

 

解說:

B和C是A的子類別

父類別的參考型態可以指向子類別態物件(因為子類別 is a 父類別)