lec2.3.1

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

     public Invoice( String part, String description, int count, double price )
     {
         partNumber = part;
         partDescription = description;
         if ( count > 0 )
             quantity = count;

         if ( price > 0.0 )
             pricePerItem = price;
      }

      public void setPartNumber( String part )
      {
          partNumber = part;
      }

      public String getPartNumber()
      {
          return partNumber;
      }

      public void setPartDescription( String description )
     {
          partDescription = description;
     }

     public String getPartDescription()
     {
         return partDescription;
     }

      public void setQuantity( int count )
      {
          if ( count > 0 )
              quantity = count;

          else if ( count <= 0 )
              quantity = 0;
      }

      public int getQuantity()
      {
          return quantity;
      }

      public void setPricePerItem( double price )
      {
          if ( price > 0.0 )
              pricePerItem = price;

          else if ( price <= 0.0 )
              pricePerItem = 0.0;
      }

      public double getPricePerItem()
      {
          return pricePerItem;
      }

      public double getInvoiceAmount()
      {
          return getQuantity() * getPricePerItem();
      }

}