discountsale.java

java编程代码

/**
 Class for a sale of one item with discount expressed as a percent of the price,
 but no other adjustments.
 Class invariant: The price is always nonnegative; the name is a
 nonempty string; the discount is always nonnegative.
*/

public class DiscountSale extends Sale
{
    private double discount; //A percent of the price. Cannot be negative.

    public DiscountSale( )
    {
        super( );
        discount = 0;
    }

    /**
     Precondition: theName is a nonempty string; thePrice is nonnegative;
     theDiscount is expressed as a percent of the price and is nonnegative.
    */
    public DiscountSale(String theName,
                                  double thePrice, double theDiscount)
    {
        super(theName, thePrice);
        setDiscount(theDiscount);
    }

    public DiscountSale(DiscountSale originalObject)
    {
        super(originalObject);
        discount = originalObject.discount;
    }

    public static void announcement( )
    {
        System.out.println("This is the DiscountSale class.");
    }

    public double bill( )
    {
        double fraction = discount/100;
        return (1 - fraction)*getPrice( );
    }

    public double getDiscount( )
    {
        return discount;
    }

    /**
     Precondition: Discount is nonnegative.
    */
    public void setDiscount(double newDiscount)
    {
        if (newDiscount >= 0)
            discount = newDiscount;
        else
        {
            System.out.println("Error: Negative discount.");
            System.exit(0);
        }
    }

    public String toString( )
    {
        return (getName( ) + " Price = $" + getPrice( )
                + " Discount = " + discount + "%\n"
                + "   Total cost = $" + bill( ));
    }

    public boolean equals(Object otherObject)
	{
	    if (otherObject == null)
	        return false;
	    else if (getClass( ) != otherObject.getClass( ))
	        return false;
	    else
	    {
	        DiscountSale otherDiscountSale =
	                         (DiscountSale)otherObject;
	        return (super.equals(otherDiscountSale)
	            && discount == otherDiscountSale.discount);
	    }
    }

    public DiscountSale clone( )
	{
	    return new DiscountSale(this );
    }
}