SCJP 1.6版考題 016

5. class Atom{
6.   Atom(){System.out.print("atom ");}
7. }
8. class Rock extends Atom{
9.    Rock(String type){System.out.print(type);}
10. }
11. public class Mountain extends Rock{
12.   Mountain(){
13.     super("granite ");
14.     new Rock("granite ");
15.   }
16.   public static void main(String[] a){new Mountain();}
17. }

What is the result?
  A. Compilation fails.
  B. atom granite
  C. granite granite
  D. atom granite granite
  E. An exception is thrown at runtime.
  F. atom granite atom granite

解答

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Ans: F

解說:

記住，
若建構子中未寫this或super的呼叫敘述，編譯器會在建構子的首行加上super()，
以此例來說，建立Mountain物件時，先叫用super(“granite”)，呼叫其父類別Rock的建構子，
此建構子會再呼叫其父類別Atom的建構子，因此，會先印出atom…