SCJP 1.6版考題 037

21. abstract class C1{
22.   public C1(){System.out.print(1);}
23. }
24. class C2 extends C1{
25.   public C2(){System.out.print(2);}
26. }
27. class C3 extends C2{
28.   public C3(){System.out.print(3);}
29. }
30. public class Ctest{
31.   public static void main(String[] a){new C3();}
32. }


What is the result?

  A. 3
  B. 23
  C. 32
  D. 123
  E. 321  
  F. Compilation fails.
  G. An exception is thrown at runtime.

解答

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Ans: D

解說:

當一個建構子中若沒有對本身建構子 (this)或父類別建構子(super)的呼叫，建構子會有一個隱含的super()，即對父類別建構子的呼叫，
因此，在建立C3物件時會呼叫C3的建構子，C3建構子會先叫用C2的建構子…