檢視 SCJP 1.6版考題 089 的原始碼

 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;

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

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

<span style="font-size:medium;"> 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)
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{{SCJP 1.6版考題講解}}