SCJP題庫第080題

3. interface Fish{}

4. class Perch implements Fish{}

5. class Walleye extends Perch{}

6. class Bluegill{}

7. public class Fisherman {

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

9.     Fish f = new Walleye();

10.   Walleye w = new Walleye()

11.   Bluegill b = new Bluegill();

12.   if(f instanceof Perch) System.out.print("f-p ");

13.   if(w instanceof Fish) System.out.print("w-f ");

14.   if(b instanceof Fish) System.out.print("b-f ");

15. }

16.}

What is the result?

A. w-f

B. f-p w-f

C. w-f b-f

D. f-p w-f b-f

E. Compilation fails.

F. An exception is thrown at runtime.

 

Ans: B

 

解說:

f instanceof Perch是判斷f所指向的物件型態是否為Perch, f是指向Walleye物件，Walleye繼承Perch，所以12行if為true

w instanceof Fish是true，w是指向Walleye物件，Walleye繼承Perch，Perch實作Fish，所以Walleye也是Fish的型態

Bluegill類別與Fish沒有任何繼承關聯，所以b instanceof Fish為false