SCJP題庫第089題

 

1. public class Car{

2.    private int wheelCount;

3.    private String vin;

4.    public Car(String vin){

5.      this.vin = vin;

6.      this.wheelCount = 4;

7.    }

8.    public String drive(){

9.      return "zoom-zoom";

10. }

11. public String getInfo(){

12.   return "VIN: " + vin + "wheels: " + wheelCount;

13. }

14.}

And:

1.   public class MeGo extends Car{

2.     public MeGo(String vin){

3.       this.wheelCount = 3;

4.     }

5. }

What two must the programmer do to correct the compilation errors? (Choose two.)

A. insert a call to this() in the Car constructor

B. insert a call to this() in the MeGo constructor

C. insert a call to super() in the MeGo constructor

D. insert a call to super(vin) in the MeGo constructor

E. change the wheelCount variable in Car to protected

F. change line 3 in the MeGo class to super.wheelCount = 3;

 

Ans: DE

 

解說:

要可以編譯必須插入super(vin)在MeGo建構子裏

因為若沒有這個呼叫，編譯器會插入一個super()在MeGo建構子裏，而Car又沒有一個有空參數的建構子，這樣會錯！

但插入super(vin)後，這個vin不是自己宣告的變數，是Car的變數，因此要把private的存取屬性換掉(public/default也可以)