// Fig. 10.12: Invoice.java
// Invoice class implements Payable.

public class Invoice implements Payable
{
   private String partNumber; 
   private String partDescription;
   private int quantity;
   private double pricePerItem;

   // four-argument constructor
   public Invoice( String part, String description, int count, 
      double price )
   {
      partNumber = part;
      partDescription = description;
      setQuantity( count ); // validate and store quantity
      setPricePerItem( price ); // validate and store price per item
   } // end four-argument Invoice constructor

   // set part number
   public void setPartNumber( String part )
   {
      partNumber = part;  
   } // end method setPartNumber

   // get part number
   public String getPartNumber()
   {
      return partNumber;
   } // end method getPartNumber

   // set description
   public void setPartDescription( String description )
   {
      partDescription = description;
   } // end method setPartDescription

   // get description
   public String getPartDescription()
   {
      return partDescription;
   } // end method getPartDescription

   // set quantity
   public void setQuantity( int count )
   {
      quantity = ( count < 0 ) ? 0 : count; // quantity cannot be negative
   } // end method setQuantity

   // get quantity
   public int getQuantity()
   {
      return quantity;
   } // end method getQuantity

   // set price per item
   public void setPricePerItem( double price )
   {
      pricePerItem = ( price < 0.0 ) ? 0.0 : price; // validate price
   } // end method setPricePerItem

   // get price per item
   public double getPricePerItem()
   {
      return pricePerItem;
   } // end method getPricePerItem

   // return String representation of Invoice object
   public String toString()
   {
      return String.format( "%s: \n%s: %s (%s) \n%s: %d \n%s: $%,.2f", 
         "invoice", "part number", getPartNumber(), getPartDescription(), 
         "quantity", getQuantity(), "price per item", getPricePerItem() );
   } // end method toString

   // method required to carry out contract with interface Payable
   public double getPaymentAmount() 
   {
      return getQuantity() * getPricePerItem(); // calculate total cost
   } // end method getPaymentAmount
} // end class Invoice


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