java 子類繼承父類成員變量的隱藏、實現方法的重寫

  成員變量的隱藏和方法的重寫

Goods.java

public class Goods {
    public double weight;
    public void oldSetWeight(double w) {
       weight=w;
       System.out.println("double型的weight="+weight);
    }
    public double oldGetPrice() {
        double price = weight*10;
        return price;
    }
}

CheapGoods.java

public class CheapGoods extends Goods {
    public int weight;
    public void newSetWeight(int w) {
       weight=w;
       System.out.println("int型的weight="+weight);
    }
    public double newGetPrice() {
        double price = weight*10;
        return price;
    }
}

Example5_3.java

public class Example5_3 {
  public static void main(String args[]) {
     CheapGoods cheapGoods=new CheapGoods();
     //cheapGoods.weight=198.98; 是非法的，因為子類對象的weight已經是int型
     cheapGoods.newSetWeight(198);
     System.out.println("對象cheapGoods的weight的值是:"+cheapGoods.weight);
     System.out.println("cheapGoods用子類新增的優惠方法計算價格："+
                         cheapGoods.newGetPrice());
     cheapGoods.oldSetWeight(198.987); //子類對象調用繼承的方法操作隱藏的double型變量weight
     System.out.println("cheapGoods使用繼承的方法（無優惠）計算價格："+
                          cheapGoods.oldGetPrice());
  }  
}

 

子類對繼承父類方法的重寫

University.java

public class University {
    void enterRule(double math,double english,double chinese) {
        double total=math+english+chinese;
        if(total>=180) 
           System.out.println("考分"+total+"達到大學最低錄取線");
        else
           System.out.println("考分"+total+"未達到大學最低錄取線");
    }
}

ImportantUniversity.java

public class ImportantUniversity extends University{
    void enterRule(double math,double english,double chinese) {
        double total=math+english+chinese;
        if(total>=220)  
           System.out.println("考分"+total+"達到重點大學錄取線");
        else
           System.out.println("考分"+total+"未達到重點大學錄取線");
    }
}

Example5_4.java

public class Example5_4 {
    public static void main(String args[]) {
       double math=64,english=76.5,chinese=66;
       ImportantUniversity univer = new  ImportantUniversity();
       univer.enterRule(math,english,chinese); //調用重寫的方法
       math=89;
       english=80;
       chinese=86;
       univer = new  ImportantUniversity();
       univer.enterRule(math,english,chinese); //調用重寫的方法
    }
}