Question

Use Java please...

Activity 1. Suppose we want to have an object-oriented design for an invoicing system, that includes invoices, one or more line items in each invoice, address of the invoice, list of products, etc. Try to design this system by indicating the required classes, responsibilities of each class, and the collaborating classes to fulfill each responsibility, and draw the CRC cards as well as UML diagram of the classes and their relationships. Then, indicate the methods of each class, provide Java documentation for each method, and then implement the classes. Beside any methods you realize, make sure you have the following functionalities for this system: • A method to format the invoice and return it as a String. • A method to compute and return the amount due of an invoice. • A method to add one LineItem object to the invoice. • A method to format a given LineItem object and return it as a String. A method to format the Address object and return it as a String. Two methods to change/set the values of description and unit price of the Product object.

Answer 1

1.

Finding Classes • Keep the following points in mind: • Class represents set of objects with the same behavior • Entities with multiple occurrences in problem description are good candidates for objects o Find out what they have in common o Design classes to capture commonalities • Represent some entities as objects, others as primitive types o Should we make a class Address or use a String? • Not all classes can be discovered in analysis phase • Some classes may already exist

2.

Case Study: Printing an Invoice – CRC Cards • Discover classes • Nouns are possible classes: Invoice Address LineItem Product Description Price Quantity Total Amount Due

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Case Study: Printing an Invoice — CRC Cards • Analyze classes: // Records the product and the quantity Invoice Address LineItem Product Description Price Quantity Total Amount Due // variable of the Product class // variable of the Product class // Not an attribute of a Product // Computed - not stored anywhere // Computed - not stored anywhere Classes after a process of elimination: Invoice Address LineItem Product

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CRC Card • Indicate what other classes are needed to fulfill responsibility (collaborators) Class Responsibilities Invoice Collaborators compute amount due LineItem

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CRC Cards for Printing Invoice Invoice and Address must be able to format themselves: Invoice format the invoice Address format the address

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CRC Cards for Printing Invoice Product and LineItem CRC cards: Product get description get unit price LineItem Product format the item get total price

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CRC Cards for Printing Invoice Invoice must be populated with products and quantities: Invoice format the invoice Address add a product and quantity LineItem Product

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Printing an Invoice — UML Diagrams Invoice Address Product LineItem Figure 7 The Relationships Between the Invoice Classes

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Method Documentation - Invoice Class /** 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 a Product, int quantity) Continued

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Method Documentation — Invoice Class (cont.) /** Formats the invoice. @return the formatted invoice */ public String format ()

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Method Documentation – LineItem Class Describes a quantity of an article to purchase and its price. public class LineItem /** Computes the total cost of this line item. @return the total price public double get Total Price () Continued

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Method Documentation – LineItem Class (cont.) /** Formats this item. @return a formatted string of this line item */ public String format ()

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Method Documentation - Product Class (cont.) Gets the product price. @return the unit price public double get Price ()

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Method Documentation - Address Class /** Describes a mailing address. public class Address /** Formats the address. @return the address as a string with three lines public String format()

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Implementation • Invoice aggregates Address and LineItem • Every invoice has one billing address • An invoice can have many line items: public class Invoice private Address billingAddress; private ArrayList<Line Item> items;

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Implementation A line item needs to store a Product object and quantity: public class Line Item private int quantity; private Product the Product;

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Implementation • The methods themselves are now very easy • Example: • getTotal Price of LineItem gets the unit price of the product and multiplies it with the quantity: Computes the total cost of this line item. @return the total price public double getTotalPrice () return the Product.getPrice () * quantity;

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2 3 This program demonstrates the invoice classes by printing a sample invoice. public class InvoicePrinter public static void main(String[] args) Address samsAddress = new Address("Sam&apos;s Small Appliances", "100 Main Street", "Anytown", "CA", "98765"); Invoice samsInvoice = new Invoice (sams Address); samsInvoice.add(new Product ("Toaster", 29.95), 3); samsInvoice.add(new Product("Hair dryer", 24.95), 1); samsInvoice.add(new Product ("Car vacuum", 19.99), 2); System.out.println(sams Invoice.format()); 20 21 }

20.

1 import java.util.ArrayList; 5 Describes an invoice for a set of purchased products. */ public class Invoice private Address billingAddress; private ArrayList<Line Item> items; Constructs an invoice. @param an Address the billing address */ public Invoice (Address anAddress) items = new ArrayList<LineItem>(); billingAddress = anAddress;

21.

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 a Product, int quantity) LineItem an Item = new LineItem (a Product, quantity); items.add (anItem);

22.

Formats the invoice. @return the formatted invoice public String format) String r = " INVOICE\n\n" + billingAddress. format () + String.format("\n\n8-30s%83%58%8s\n", "Description", "Price", "Oty", "Total"); for (LineItem item : items) r = r + item.format() + "\n"; r = r + String.format("\nAMOUNT DUE: $%8.2f", get Amount Due ()); return r;

23.

Computes the total amount due. @return the amount due public double getAmount Due() double amount Due = 0; for (LineItem item : items) amount Due = amount Due + item.getTotal Price(); return amount Due; 66 )

1 ** 2 Describes a quantity of an article to purchase. 3 */ 4 public class Line Item 5 private int quantity; private Product the Product; Constructs an item from the product and quantity @param a Product the product @param aQuantity the item quantity public LineItem(Product a Product, int aQuantity) the Product = aProduct; quantity aQuantity;

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25.

Computes the total cost of this line item. @return the total price public double getTotalPrice () return the product.getPrice() * quantity; Formats this item @return a formatted string of this item public String format () return String.format("%-30s%8.285d8.2f", the Product.get Description(), the Product.getPrice (), quantity, get TotalPrice () ); 38 39

2 3 Describes a product with a description and a price. */ public class Product private String description; private double price; Constructs a product from a description and a price. @param aDescription the product description @param aPrice the product price public Product (String a Description, double a Price) description = a Description; price = a Price;

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27.

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;

28.

1 ** 2 3 Describes a mailing address. */ public class Address 4 private String name; private String street; private String city; private String state; private String zip; 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 a City, String aState, String a Zip) name = aName; street = aStreet; city = aCity; state = a State; zip = a Zip; Formats the address. @return the address as a string with three lines public String format() 35 return name + "\n" + street + "\n" + city + ", " + state + " " + zip; 39 40