SCJP 1.6版考題 089

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;

解答

---

Ans: D E

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)