SCJP題庫第014題

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.

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(){}

}