SCJP 1.6版考題 014

11. class Person{
12.   String name = "No name";
13.   public Person(String nm){name = nm;}
14. }
15.
16. class Employee extends Person{
17.   String empID = "0000";
18.   public Employee(String id){empID = id;}
19. }
20.
21. class EmployeeTest{
22.   public static void main(String[] args){
23.     Employee e = new Employee("4321");
24.     System.out.println(e.empID);
25.   }
26. }

What is the result? 
  A. 4321
  B. 0000
  C. An exception is thrown at runtime.
  D. Compilation fails because of an error in line 18.

解答

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Ans: D

解說:

下面二個方法以第2種方法較好，記得有一個黃金定律，一個類別裏，不管如何，都要有一個無參數的建構子…！
1.
 class Employee extends Person{
   String empID = "0000";
   public Employee(String id){super(id); empID = id;}
 }

2.
 class Person{
   String name = "No name";
   public Person(String nm){name = nm;}
   public Person(){}
 }

Ans:D 解說: