Ikk：新頁面: 1. class Super{ 2. private int a; 3. protected Super(int a){this.a = a;} 4. } ... 11. class Sub extends Super{ 12. public Sub(int a){super(a);} 13. public Sub(){this.a ...

2013-03-30T08:38:58Z

新頁面: 1. class Super{ 2. private int a; 3. protected Super(int a){this.a = a;} 4. } ... 11. class Sub extends Super{ 12. public Sub(int a){super(a);} 13. public Sub(){this.a ...

新頁面

1. class Super{
2. private int a;
3. protected Super(int a){this.a = a;}
4. }
...
11. class Sub extends Super{
12. public Sub(int a){super(a);}
13. public Sub(){this.a = 5;}
14. }

Which two, independently, will allow Sub to compile? (Choose two.)

A. Change line 2 to:
public int a;

B. Change line 2 to:
protected int a;

C. Change line 13 to:
public Sub(){this(5);}

D. Change line 13 to:
public Sub(){super(5);}

E. Change line 13 to:
public Sub(){super(a);}

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

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

<span style="font-size:medium;"> 解說:
<BR>[[檔案:SCJP18.png]]
<BR>
上面的程式會發生二個編譯上的錯誤，
第一錯誤是：第13行，會自動地被javac加入一個super()呼叫，而super類別中又沒有無參數的建構子。
第二個錯誤是this.a會存取到super中私有的a，造成錯誤！

A/B將super中的a存取屬性改成public/protected僅修正第2個錯誤，第1個錯誤還在
E修正了第1個問題，但第2個問題依然存在。

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{{SCJP 1.6版考題講解}}

SCJP 1.6版考題 018 - 修訂歷史

Ikk：新頁面: 1. class Super{ 2. private int a; 3. protected Super(int a){this.a = a;} 4. } ... 11. class Sub extends Super{ 12. public Sub(int a){super(a);} 13. public Sub(){this.a ...