Ikk：新頁面: 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) ...

2013-03-30T06:12:18Z

新頁面: 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) ...

新頁面

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.

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<span style="font-size:medium;">解答</span>

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<span style="font-size: medium;">Ans: B </span>

<span style="font-size:medium;"> 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

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{{SCJP 1.6版考題講解}}

SCJP 1.6版考題 080 - 修訂歷史

Ikk：新頁面: 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) ...