Question

Java

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.

Activity 2.

In the previous activity, you completed the invoice creation and print tasks. Now, suppose that you want an extra functionality into the requirements as follows: You are asked to keep the available quantity of every product, and at the time of creating a new line item, you should check if enough number of quantity of the given product is available. Otherwise, you should change a flag for that product that indicates “OutOfStock” and ignore adding the new line item into the invoice. Try to modify the corresponding classes to fulfill this new requirement.

Answer 1

Below is my Java code. The out of stock feature asked in Activity 2 is implemented in the "addLineItem" function of the "Invoice" class.

import java.io.*;
import java.util.*;

class Product {
int id, quantitiy_in_stock, price;
boolean out_of_stock;

Product(int i, int q, int p) {
this.id = i;
this.quantitiy_in_stock = q;
this.price = p;

if (q > 0) {
this.out_of_stock = false;
}
else {
this.out_of_stock = true;
}
}
}

class LineItem {
Product product;
int quantity, amount;

LineItem(Product p, int q) {
this.product = p;
this.quantity = q;
this.amount = p.price * q;
}
}

class Invoice {
List<LineItem> lineItemList;

Invoice() {
this.lineItemList = new ArrayList<>();
}

void addLineItem(Product product, int quantity) {
if ((product.out_of_stock) || (product.quantitiy_in_stock < quantity)) {
product.out_of_stock = true;
}
else {
this.lineItemList.add(new LineItem(product, quantity));
}
}
}