This is Shopping Cart Code

Item.java

class Item {
	private String productName;
	private int quantity;
	private double unitPrice;
	Item(String productName, int quantity, double unitPrice) {
		this.productName = productName;
		this.quantity = quantity;
		this.unitPrice = unitPrice;
	}
	public String toString() {
		String s = this.productName + ":";
		s = s + this.quantity + "\n";
		return s;
	}
	public String getProductName() {
		return this.productName;
	}
	public int getQuantity() {
		return this.quantity;
	}
	public double getUnitPrice() {
		return this.unitPrice;
	}
}

ShoppinCartTest.java

/**
 *
 * ShoppingCartTest has a main method and you cannot make changes to it.
 * You have to implement Item and ShoppingCart classes for the main method to work
 * Item class should have a constructor with 3 arguments. (product name, quantity, unit price)
 * Shopping Cart should hold all the items the user wants to buy
 * It should implement addToCart, removeFromCart, printInvoice, applyCoupon methods.
 * It should also implement getTotalAmount, getPayableAmount
 * Sales tax is 14% of the total amount and it should be printed on the invoice
 * On applying coupon IND10, 10% discount should be applied to the cart
 * No other copon codes are allowed
 * 
 */

public class ShoppingCartTest
{
  public static void main(String[] args)
  {
    // creates new items with product name, quantity and unit price
    Item i1 = new Item("Olive Oil 1l", 3, 100.0);
    Item i2 = new Item("Cheese Slices", 2, 50.0);
    Item i3 = new Item("Bread", 1, 75.0);
    Item i4 = new Item("Eggs", 50, 10.0);
    Item i5 = new Item("Chicken Salami", 2, 100.0);
    
    ShoppingCart cart = new ShoppingCart();
    
    /* add the item to the cart */
    cart.addToCart(i1);
    cart.addToCart(i2);
    cart.addToCart(i3);
    cart.addToCart(i4);
    cart.addToCart(i5);
    
    /*
     * shows the list of items in the cart with quantity
     * Expected Output to the console:
     * Olive Oil 1l: 3
     * Cheese Slices: 2
     * Bread: 1
     * Eggs: 50
     * Chicken Salami: 2
     */
    cart.showCart();
    
    /* remove the item sent as argument from the cart */
    cart.removeFromCart(i3);    
    
    /*
     * shows the list of items in the cart with quantity
     * Expected Output to the console:
     * Olive Oil 1l: 3
     * Cheese Slices: 2
     * Eggs: 50
     * Chicken Salami: 2
     */
    cart.showCart();

    /*
     * gets the total amount for the items in the cart
     * Expected Output:
     * 1100
     */
    double totalAmount = cart.getTotalAmount();
    System.out.println(totalAmount);

    /*
     * Gets the payable amount,
     * it deduct discount and add tax to the total amount of items in cart
     * Expected Output:
     * 1254
     */
    double payableAmount = cart.getPayableAmount();
    System.out.println(payableAmount);    

    /* apply a coupon code */
    cart.applyCoupon("IND50");
    
    /* 
     * print the items with the quanity, unit price, total amount
     * apply coupon if valid 
     * add tax to the total amount after discount
     * Expected Output to the console:
     * Olive Oil 1l      3    100.00    300.00 
     * Cheese Slices     2     50.00    100.00
     * Eggs             50     10.00    500.00
     * Chicken Salami    2    100.00    200.00
     *                          Total: 1100.00
     *                          Disc%:    0.00
     *                          Tax:    154.00
     *                          Total: 1254.00
     *
     */
   cart.printInvoice();

    cart.applyCoupon("IND10");

    /* 
     * print the items with the quanity, unit price, total amount
     * apply coupon if valid 
     * add tax to the total amount after discount
     * Expected Output to the console:
     * Olive Oil 1l      3    100.00    300.00 
     * Cheese Slices     2     50.00    100.00
     * Eggs             50     10.00    500.00
     * Chicken Salami    2    100.00    200.00
     *                          Total: 1100.00
     *                          Disc%:  110.00
     *                          Tax:    154.00
     *                          Total: 1128.60
     *
     */
    cart.printInvoice();

    cart.addToCart(new Item("Milk", 5, 30.00));
    /* 
     * print the items with the quanity, unit price, total amount
     * apply coupon if valid 
     * add tax to the total amount after discount
     * Expected Output to the console:
     * Olive Oil 1l      3    100.00    300.00 
     * Cheese Slices     2     50.00    100.00
     * Eggs             50     10.00    500.00
     * Chicken Salami    2    100.00    200.00
     * Milk              5     30.00    150.00
     *                          Total: 1250.00
     *                          Disc%:  125.00
     *                          Tax:    157.50
     *                          Total: 1282.50
     *
     */
    cart.printInvoice();
  }
}

ShoppingCat.java

import java.util.ArrayList;
import java.util.ListIterator;
class ShoppingCart {
	ArrayList<Item> item;
	double totalAmount;
	double payableAmount;
	double discount;
	double tax;
	String coupon;
	ShoppingCart() {
		this.item = new ArrayList<Item>();
		this.coupon = "";
		this.totalAmount = 0;
		this.payableAmount = 0;
		this.discount = 0;
		this.tax = 0;
	}
	public void addToCart(Item item) {
		this.item.add(item);
	}
	public void showCart() {
		ListIterator<Item> iterator = item.listIterator();
		while(iterator.hasNext()) {
			Item item1 = iterator.next();
			System.out.println(item1);
		}
	}
	public void removeFromCart(Item i) {
		ListIterator<Item> iterator1 = item.listIterator();
		while(iterator1.hasNext()) {
			Item item2 = iterator1.next();
			if (item2.getProductName().equals(i.getProductName())) {
				this.item.remove(i);
				break;
			}
		}
	}
	public double getTotalAmount() {
		ListIterator<Item> iterator2 = item.listIterator();
		this.totalAmount = 0;
		while(iterator2.hasNext()) {
			Item item3 = iterator2.next();
			this.totalAmount = this.totalAmount + (item3.getUnitPrice() * item3.getQuantity());
		}
		return this.totalAmount;
	}
	public void applyCoupon(String coupon) {
		this.coupon = coupon;
		if (coupon.equals("IND10")) {
			this.discount = this.getTotalAmount() * (0.1);
			this.totalAmount = this.totalAmount - this.discount;
		} else {
			this.totalAmount = this.totalAmount;
		}
	}
	public double getPayableAmount() {
		this.payableAmount = 0;
		this.tax = this.totalAmount * (0.14);
		this.payableAmount = this.totalAmount + this.tax;
		return this.payableAmount;
	}
	public void printInvoice() {
		ListIterator<Item> iterator3 = item.listIterator();
		while(iterator3.hasNext()) {
			Item item4 = iterator3.next();
			System.out.print(item4.getProductName() + "\t");
			System.out.print(item4.getQuantity() + "\t");
			System.out.print(item4.getUnitPrice() + "\t");
			System.out.println(item4.getUnitPrice() * item4.getQuantity());
		}
		System.out.println("\t\t\t" + "Total    : " + this.getTotalAmount());
		this.applyCoupon(this.coupon);
		System.out.println("\t\t\t" + "Discount : " + this.discount);
		this.getPayableAmount();
		System.out.println("\t\t\t" + "Tax      : " + this.tax);
		System.out.println("\t\t\t" + "Total    : " + this.getPayableAmount());
	}
}

How do i run this files as they are all separated

1. put all files in one directory.
2. navigate to that directory in a terminal
3. compile with javac *.java
4. run with java ShoppingCartTest

How do i run this files as they are all separated

Or you can re-write so you can familiarize the code.