Question

Java program Statement: Provide a user interface to the invoice program in Section 12.3 that allows a user to enter and print an arbitrary invoice. Do not modify any of the existing classes.

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/**

   Describes an invoice for a set of purchased products. 

*/

public class Invoice

{  

   /**

      Adds a charge for a product to this invoice. 

      @param aProduct the product that the customer ordered 

      @param quantity the quantity of the product 

   */

   public void add(Product aProduct, int quantity)

   { 

   }

   /**

      Formats the invoice. 

      @return the formatted invoice 

   */

   public String format()

   { 

   }

}

/**

   Describes a quantity of an article to purchase. 

*/

public class LineItem

{ 

   /**

      Computes the total cost of this line item. 

      @return the total price 

   */

   public double getTotalPrice()

   { 

   }

   /**

      Formats this item. 

      @return a formatted string of this item 

   */

   public String format()

   { 

   }

}

/**

   Describes a product with a description and a price. 

*/

public class Product

{ 

   /**

      Gets the product description. 

      @return the description 

   */

   public String getDescription()

   { 

   }

   /**

      Gets the product price. 

      @return the unit price 

   */

   public double getPrice()

   {

   }

}

/**

   Describes a mailing address. 

*/

public class Address

{ 

   /**

      Formats the address. 

      @return the address as a string with three lines 

   */

   public String format()

   { 

   }

}

Answer 1

public class Invoice
{
/**
Adds a charge for a product to this invoice.
@param aProduct the product that the customer ordered
@param quantity the quantity of the product
*/
public void add(Product aProduct, int quantity)
{ LineItem anItem = newLineItem(aProduct, quantity);
items.add(anItem);
}

/**
Formats the invoice.
@return the formatted invoice
*/
public String format()
{
String r = " I N V O I C E\n\n"
+ billingAddress.format()
+ String.format("\n\n%-30s%8s%5s%8s\n",
"Description", "Price", "Qty", "Total");

for (LineItem i : items)
{
r = r + i.format() + "\n";
}

r = r + String.format("\nAMOUNT DUE: $%8.2f", getAmountDue());

return r;
}

/**
Describes a quantity of an article to purchase.
*/
public class LineItem
{
/**
Constructs an item from the product and quantity.
@param aProduct the product
@param aQuantity the item quantity
*/
public LineItem(Product aProduct, int aQuantity)
{
theProduct = aProduct;
quantity = aQuantity;
}

/**
Computes the total cost of this line item.
@return the total price
*/
public Money getTotalPrice()
{
Money m = theProduct.getPrice();
for (int i = 2; i <= quantity; i++)
m.add(theProduct.getPrice());
return m;
}

/**
Formats this item.
@return a formatted string of this item
*/
public String format()
{
return String.format("%-30s%8s%5d%8s",
theProduct.getDescription(), theProduct.getPrice().format(),
quantity, getTotalPrice().format());
}

private int quantity;
private Product theProduct;
}

/**
Describes a product with a description and a price.
*/
public class Product
{
/**
Constructs a product from a description and a price.
@param aDescription the product description
@param aPrice the product price
*/
public Product(String aDescription, Money aPrice)
{
description = aDescription;
price = aPrice;
}

/**
Gets the product description.
@return the description
*/
public String getDescription()
{
return description;
}

/**
Gets the product price.
@return the unit price
*/
public double getPrice()
{
return price;
}

private String description;
private double price;
}

/**
Describes a mailing address.
*/
public class Address
{
/**
Constructs a mailing address.
@param aName the recipient name
@param aStreet the street
@param aCity the city
@param aState the two-letter state code
@param aZip the ZIP postal code
*/
public Address(String aName, String aStreet,
String aCity, String aState, String aZip)
{
name = aName;
street = aStreet;
city = aCity;
state = aState;
zip = aZip;
}   

/**
Formats the address.
@return the address as a string with three lines
*/
public String format()
{
return name + "\n" + street + "\n"
+ city + ", " + state + " " + zip;
}

private String name;
private String street;
private String city;
private String state;
private String zip;
}

I hope it helps. Refer screenshot for better understanding of syntax