我正在写一个名为 discount.java 的 class，我在处理数量和价格的负值时遇到问题

Question

正如我提到的，我正在编写一个名为 discount.java 和 TestDiscount.java 的 class；到目前为止一切正常，但当数量或价格和负值时，我在获取错误消息而不是实际值时遇到问题。这里有一些关于所需输出和我到目前为止所做的更多信息：

输出必须是以下形式：

数量为：xx 单价为：$xx.xx 折扣为：$xx.xx

或

数量为：-xx 数量为负数。无法计算折扣

或

数量为：150 单价为：-$15.00 钱为负数，不能计算折扣金额

    public class discount {


     int quantity;
     double price;
     public static int NINETY_NINE = 99;
     public static int TWENTY = 20;
     private static int TEN = 10, FORTY_NINE = 49;
     public static double TEN_PERCENT = 0.10, FIVE_PERCENT = 0.05, 
             TWO_PERCENT = 0.02, THREE_PERCENT = 0.03, ONE_PERCENT = 0.01 ;
     private double discount;
    // public static double discount_amount = discount * quantity * price;


    discount(int quantity, double price)
    {
          double discount = 0;
         //double d = discount;
           this.quantity = quantity;
           this.price = price;
     }
     boolean quantityOutOfRange()
     {
        return quantity < 0;
     }
     boolean priceOutOfRange()
    {
         return price  <  0;
    }
     public double getDiscount()
    {
       return discount;
    }

    public int getQuantity()
    {
        return quantity;
    }

    public double getUnitPrice()
    {
        return price;
    }



   public void calculate()
   {
      if (quantity > NINETY_NINE)
     {
         if (price > TWENTY)
                discount = TEN_PERCENT;

         else if ( price > TEN)
                 discount = FIVE_PERCENT;
        else
                discount = TWO_PERCENT; 
     }
     else if (quantity > FORTY_NINE)
     {
    // calculate discount
         if (price > TWENTY)
                discount = THREE_PERCENT;
         else if ( price > TEN)
                 discount = TWO_PERCENT;
        else
                discount = ONE_PERCENT; 
     }
     else
     {
    // calculate discount
         if (price > TWENTY)
                discount = TWO_PERCENT;
         else if ( price > TEN)
                 discount = ONE_PERCENT;
        else
                discount = 1;   
     }
     if (quantity < 0)
         {
            System.out.println("Quantity is negative. Cannot compute discount");
         }
    //double discount_amount = discount * quantity * price;  

   }

}



public class TestDiscount {

    public static void main(String[] arg) {

      String input = JOptionPane.showInputDialog("Enter the quantity desired "
                + ", and unit price "
                + "\n(Separated by spaces)");

        Scanner in = new Scanner(input);

        int quantity = in.nextInt();
        double price = in.nextDouble();

        discount current = new discount(quantity, price);
        current.calculate();
        System.out.println("\nDiscounts:\n");
        System.out.println("The quantity is: " + current.getQuantity()+ "\tThe unit price is = $ " + current.getUnitPrice() + 
                "\tThe discount is = $ " + current.getQuantity()* current.getUnitPrice() * current.getDiscount());
        System.exit(0) ;
    }
   }

Answer 1

创建名为 like 的新方法

public boolean validated() {

  boolean ok = true;

  if (quantity < 0)
     {
        System.out.println("Quantity is negative. Cannot compute 
                             discount");
        ok = false;
     }

  if (price< 0)
     {
        System.out.println("Price is negative. Cannot compute 
                            discount");
        ok = false;
     }

   return ok;

}

然后在main

discount current = new discount(quantity, price);
if (current.validated ()) {
   current.calculate ();
}

Answer 2

在计算方法中首先检查负值

if (quantity < 0)
 {
    System.out.println("error message");
 }

if (price < 0)
 {
    System.out.println("error message"); 
 }

我正在写一个名为 discount.java 的 class，我在处理数量和价格的负值时遇到问题

Im writing a class called discount.java and i am having issues processing negative values for quantity and price

java

exception-handling

negative-number

discount