Question

我试图将补货费用放在DVD子类movieTitle中。编辑我的代码应该是它的方式，但它不起作用。 DVD是父类，movieTitle是子类。我试图从子类到父类获得方法补货费...请帮忙。我不知道如何从子类调用该方法在需要打印出来的父类中可用。我找到了解释子类和继承的地方，但没有找到如何实现子类的功能（方法）。

线程“main”中的异常java.lang.RuntimeException：无法编译的源代码 - 错误的sym类型：inventoryprogrampart3.DVD.movieTitle.restockFee 在inventoryprogrampart3.DVD.toString（DVD.java:126）

说明：

通过创建产品类的子类来修改库存程序，该子类使用您选择的产品的另一个独特功能（例如，对于DVD子类，您可以使用电影标题）。在子类中，创建一个方法来计算产品库存的值，该方法的名称与先前为产品类创建的方法相同。子类方法还应该为该产品的库存价值增加5％的重新进货费用。修改输出以显示您选择的此附加功能和重新进货费用。

 <code>
 import java.util.Arrays;
 public class InventoryProgramPart3 {


 public static void main(String[] args) {



  DVD[] myDVD = new DVD[5]; // create array of DVD's

  // inventory of DVD's
   DVD p1 = new DVD ( 1, "Fast and Furious 6", 8, 5 );
   DVD p2 = new DVD ( 2, "The Matrix Reloaded", 8, 5 );
   DVD p3 = new DVD ( 3, "In Pursuit of Happiness", 8, 5 );
   DVD p4 = new DVD ( 4, "Darknet", 8, 5 );
   DVD p5 = new DVD ( 5, "Goonies", 8, 5 );


  myDVD[0] = p1;
  myDVD[1] = p2;
  myDVD[2] = p3;
  myDVD[3] = p4;
  myDVD[4] = p5;


         double total = 0.0;
  for (int i = 0; i < 5; i++)

    { 
    total +=  myDVD[i].getInvValue(); 
  }

    // Display the total value of the inventory on the screen

 //sorting DVD's alphabetically
 Arrays.sort(myDVD);

 for(DVD s: myDVD)

     {
 System.out.println(s);
 }

 System.out.println();
 System.out.printf("Total value of the entire inventory is: $ %.2f", total); 
 System.out.println();

 } // end main method
 }//end class 





 package inventoryprogrampart3;

 @SuppressWarnings("rawtypes")
 class DVD implements Comparable

 {
 private String thisTitle;
 private double thisStock;
 private double thisPrice;
 private double thisItem; 


 public DVD( double item, String title, double stock, double price )

 {
 thisItem = item;
 thisTitle = title;
 thisStock = stock;
 thisPrice = price;
 }// end constuctor

 // Getters and setters        

 public void setTitle(String title)

    {
thisTitle = title;
}//end method setTitle


//return Title
public String getTitle()

    {
return thisTitle;
}//end method getTitle

//set Stock
public void setStock(double stock)

    {
thisStock = stock;
}//end method setStock

//return Stock
public double getStock()

    {
return thisStock;
}//end method get Stock

public void setPrice(double price)

    {
thisPrice = price;
}//end method setPrice

//return Price
public double getPrice() 

    {
return thisPrice;
}//end method getPrice

public void setItem(double item)

    {
thisItem = item;
}//end method setItem

//return Item
public double getItem()

    {
return thisItem;
}//end method getItem

//calculate the inventory value
public double value()

    {
return thisPrice * thisStock;
}//end method value

public double getInvValue()

    {
    double invValue = 0;
    for(int i = 0; i < 5; i++)
        {
         invValue = value();
        }
    return invValue;        
    }

    @Override
public int compareTo (Object o)

    {
 DVD s = (DVD)o;
 return thisTitle.compareTo(s.getTitle());
 }

     @Override
public String toString() // 



    {
  System.out.println();
 **return "Item number is: \t\t" + thisItem + "\nProducts Title is: \t\t"+ 
 thisTitle+"\nPrice: \t\t\t\t$" + thisPrice + "\nQuantity: \t\t\t"
             + thisStock + "\nValue: \t\t\t\t$" + value() + "\nRestock fee: 
  \t\t\t$" + restockFee()  ;**   <-- error here..........
   restock method is in the subclass (movieTitle), and do not not how to    
   implement it here in the parent class. 


    }         //end main method
    }        // End DVD class



package inventoryprogrampart3;

class movieTitle extends DVD {

private double thisRestockFee;// Restock fee to add to the inventory value

public movieTitle(double item, String title, double stock,
        double price, double restockFee) 
{
    super(item, title, stock, price);
    thisRestockFee = restockFee;
}


public double restockFee() {
    return super.getPrice() * .05;
}// end method value
} // End movieTitle class

</code>

Answer 1

制作DVD摘要并将restockFee更改为这样

public abstract double restockFee();

现在movieTitle看起来应该是这样的

class movieTitle extends DVD {

    private double restockFee1;// Restock fee to add to the inventory value

    public movieTitle(double item, String title, double stock,
            double price, double restockFee) {
        super(item, title, stock, price);
        this.restockFee1 = restockFee;
    }

    @Override
    public double restockFee() {
        return super.getPrice() * restockFee1;
    }// end method value
} // End movieTitle class

由于super还没有实现restockFee，因此它将调用child的实现。并且在测试中使用movieTitle。

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