檢視 SCJP 1.6版考題 014 的原始碼

 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.



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

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

<span style="font-size:medium;"> 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(){}
  }

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{{SCJP 1.6版考題講解}}
Ans:D
解說: