Ikk：新頁面: Given: 1. public class A { 2. 3. private int counter = 0; 4 5. public static int getInstanceCount(){ 6. return counter; 7. } 8. 9. public A(){ 10. counter++; 11. } 12. 13...

2013-03-30T05:37:00Z

新頁面: Given: 1. public class A { 2. 3. private int counter = 0; 4 5. public static int getInstanceCount(){ 6. return counter; 7. } 8. 9. public A(){ 10. counter++; 11. } 12. 13...

新頁面

Given:
1. public class A {
2.
3. private int counter = 0;
4
5. public static int getInstanceCount(){
6. return counter;
7. }
8.
9. public A(){
10. counter++;
11. }
12.
13. }

And given this code from Class B:
25. A a1 = new A();
26. A a2 = new A();
27. A a3 = new A();
28. System.out.println(A.getInstanceCount());

What is the result?
A. Compilation of class A fails.
B. Line 28 prints the value 3 to System.out.
C. Line 28 prints the value 1 to System.out.
D. A runtime error occurs when line 25 executes.
E. Compilation fails because of an error on line 28.

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

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

<span style="font-size:medium;"> 解說:
getInstanceCount是類別A的類別成員方法，在類別方法中要存取非類別成員counter，即物件成員，
先要建立物件或以一個明確的物件參考存取counter物件變數
第6行須改為return new A().counter;

</span>
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{{SCJP 1.6版考題講解}}

SCJP 1.6版考題 105 - 修訂歷史

Ikk：新頁面: Given: 1. public class A { 2. 3. private int counter = 0; 4 5. public static int getInstanceCount(){ 6. return counter; 7. } 8. 9. public A(){ 10. counter++; 11. } 12. 13...