public class GroceryStore {
    
    // instance variables
    Clerk myClerk;
    public int KINDS_OF_ITEMS = 4;
    public GroceryItem[ ] item = new GroceryItem[KINDS_OF_ITEMS];
    public int[ ] itemCount = new int[KINDS_OF_ITEMS];
    double money = 1000.00;
    
    // constructor
    GroceryStore() {
        item[0] = new GroceryItem("milk", 2.12);
        item[1] = new GroceryItem("butter", 2.50);
        item[2] = new GroceryItem("eggs", 0.89);
        item[3] = new GroceryItem("bread", 1.59);
        for (int i = 0; i < KINDS_OF_ITEMS; i++) {
            itemCount[i] = 50;  // the store has lots of everything
        }
    }
    
    public static void main(String args[]) {
        GroceryStore store = new GroceryStore();
        Clerk clerk = new Clerk();
        store.hire(clerk);
        Customer customer = new Customer();
        customer.shop(store);
    }
    
    public void hire(Clerk clerk) {
        myClerk = clerk;
        clerk.takePosition(this); // "this" = this store
    }
    
    public Clerk getClerk() {
        return myClerk;
    }
}

import java.util.*; // for Random

public class Customer {
    
    GroceryItem[ ] myShoppingBasket = new GroceryItem[20];
    Random random = new Random();
    double myMoney = 100.00;
    
    public void shop(GroceryStore store) {
        selectGroceries(store); // because the store holds the groceries
        checkOut(store);
    }
    
    public void selectGroceries(GroceryStore store) {
        int itemsInMyBasket = 0;
        for (int i = 0; i < store.KINDS_OF_ITEMS; i++) { // for each kind of item
            for (int j = 0; j < 3; j++) {                // choose up to 3 of it
                if (random.nextInt(2) == 1) {
                    myShoppingBasket[itemsInMyBasket] = store.item[i];
                    store.itemCount[i] = store.itemCount[i] - 1;
                    itemsInMyBasket = itemsInMyBasket + 1;
                }
            }
        }
    }
    
    void checkOut(GroceryStore  store) {
        Clerk clerk = store.getClerk();
        double total = clerk.ringUp(myShoppingBasket);
        myMoney = myMoney - total;
        clerk.pay(total);
    }
}

public class Clerk {

    GroceryStore myStore;

    public void takePosition(GroceryStore store) {
        myStore = store;
    }
    
    public double ringUp(GroceryItem[] item) {
        double total = 0;
        int itemNumber = 0;
        while (item[itemNumber] != null) {
            total = total + item[itemNumber].price;
            System.out.println(item[itemNumber].name + "     " +
                               item[itemNumber].price);
            itemNumber = itemNumber + 1;
        }
        System.out.println("TOTAL     " + total);
        return total;
    }
    
    public void pay(double amount) {
        myStore.money = myStore.money + amount;
    }
}

public class GroceryItem {

    // Instance variables
    public String name;
    public double price;
    
    // Constructor
    GroceryItem(String name, double price) {
        this.name = name;
        this.price = price;
    }
}

milk     2.12
butter     2.5
butter     2.5
eggs     0.89
eggs     0.89
TOTAL     8.9