Iterator Pattern

Abstractions

public interface Iterator {
// this one is generic. Built-in has method remove()
// we will use built in
	boolean hasNext();
	Object next();
}

public interface Menu {
	public Iterator createIterator();
}

public class MenuItem {
	String name;
	String description;
	boolean vegetarian;
	double price;
 
	public MenuItem(String name, 
	                String description, 
	                boolean vegetarian, 
	                double price) 
	{
		this.name = name;
		this.description = description;
		this.vegetarian = vegetarian;
		this.price = price;
	}
  
	public String getName() {
		return name;
	}
  
	public String getDescription() {
		return description;
	}
  
	public double getPrice() {
		return price;
	}
  
	public boolean isVegetarian() {
		return vegetarian;
	}
	public String toString() {
		return (name + ", $" + price + "\n   " + description);
	}
}

Implementations

public class DinerMenuIterator implements Iterator {
	MenuItem[] list;
	int position = 0;
 
	public DinerMenuIterator(MenuItem[] list) {
		this.list = list;
	}
 
	public Object next() {
		MenuItem menuItem = list[position];
		position = position + 1;
		return menuItem;
	}
 
	public boolean hasNext() {
		if (position >= list.length || list[position] == null) {
			return false;
		} else {
			return true;
		}
	}
  
	public void remove() {
		//throw new UnsupportedOperationException(
		//	"Alternating Diner Menu Iterator does not support remove()");

		if (position <= 0) {
			throw new IllegalStateException
				("You can't remove an item until you've done at least one next()");
		}
		if (list[position-1] != null) {
			for (int i = position-1; i < (list.length-1); i++) {
				list[i] = list[i+1];
			}
			list[list.length-1] = null;
		}
	}
}

public class DinerMenu implements Menu {
	static final int MAX_ITEMS = 6;
	int numberOfItems = 0;
	MenuItem[] menuItems;
  
	public DinerMenu() {
		menuItems = new MenuItem[MAX_ITEMS];
 
		addItem("Vegetarian BLT",
			"(Fakin') Bacon with lettuce & tomato on whole wheat", true, 2.99);
		addItem("BLT",
			"Bacon with lettuce & tomato on whole wheat", false, 2.99);
		addItem("Soup of the day",
			"Soup of the day, with a side of potato salad", false, 3.29);
		addItem("Hotdog",
			"A hot dog, with saurkraut, relish, onions, topped with cheese",
			false, 3.05);
		addItem("Steamed Veggies and Brown Rice",
			"A medly of steamed vegetables over brown rice", true, 3.99);
		addItem("Pasta",
			"Spaghetti with Marinara Sauce, and a slice of sourdough bread",
			true, 3.89);
	}
  
	public void addItem(String name, String description, 
	                     boolean vegetarian, double price) 
	{
		MenuItem menuItem = new MenuItem(name, description, vegetarian, price);
		if (numberOfItems >= MAX_ITEMS) {
			System.err.println("Sorry, menu is full!  Can't add item to menu");
		} else {
			menuItems[numberOfItems] = menuItem;
			numberOfItems = numberOfItems + 1;
		}
	}
 
	public MenuItem[] getMenuItems() {
		return menuItems;
	}
  
	public Iterator createIterator() {
		return new DinerMenuIterator(menuItems);
		//return new AlternatingDinerMenuIterator(menuItems);
	}
 
	// other menu methods here
}

import java.util.ArrayList;
import java.util.Iterator;

public class PancakeHouseMenu implements Menu {
	ArrayList menuItems;
 
	public PancakeHouseMenu() {
		menuItems = new ArrayList();
    
		addItem("K&B's Pancake Breakfast", 
			"Pancakes with scrambled eggs, and toast", 
			true,
			2.99);
 
		addItem("Regular Pancake Breakfast", 
			"Pancakes with fried eggs, sausage", 
			false,
			2.99);
 
		addItem("Blueberry Pancakes",
			"Pancakes made with fresh blueberries, and blueberry syrup",
			true,
			3.49);
 
		addItem("Waffles",
			"Waffles, with your choice of blueberries or strawberries",
			true,
			3.59);
	}

	public void addItem(String name, String description,
	                    boolean vegetarian, double price)
	{
		MenuItem menuItem = new MenuItem(name, description, vegetarian, price);
		menuItems.add(menuItem);
	}
 
	public ArrayList getMenuItems() {
		return menuItems;
	}
  
	public Iterator createIterator() {
		// no need to implenet own Iterator - java.util is ok for ArrayList		
		return menuItems.iterator();
	}
  
	// other menu methods here
}

import java.util.*;

public class CafeMenu implements Menu {
	Hashtable menuItems = new Hashtable();
  
	public CafeMenu() {
		addItem("Veggie Burger and Air Fries",
			"Veggie burger on a whole wheat bun, lettuce, tomato, and fries",
			true, 3.99);
		addItem("Soup of the day",
			"A cup of the soup of the day, with a side salad",
			false, 3.69);
		addItem("Burrito",
			"A large burrito, with whole pinto beans, salsa, guacamole",
			true, 4.29);
	}
 
	public void addItem(String name, String description, 
	                     boolean vegetarian, double price) 
	{
		MenuItem menuItem = new MenuItem(name, description, vegetarian, price);
		menuItems.put(menuItem.getName(), menuItem);
	}
 
	public Hashtable getItems() {
		return menuItems;
	}
  
	public Iterator createIterator() {
		// need to return values() for creating iterator over arraylist
		return menuItems.values().iterator();
	}
}

import java.util.Iterator;
  
public class Waitress {
	Menu pancakeHouseMenu;
	Menu dinerMenu;
	Menu cafeMenu;
 
	public Waitress(Menu pancakeHouseMenu, Menu dinerMenu, Menu cafeMenu) {
		this.pancakeHouseMenu = pancakeHouseMenu;
		this.dinerMenu = dinerMenu;
		this.cafeMenu = cafeMenu;
	}
 
	public void printMenu() {
		Iterator pancakeIterator = pancakeHouseMenu.createIterator();
		Iterator dinerIterator = dinerMenu.createIterator();
		Iterator cafeIterator = cafeMenu.createIterator();

		System.out.println("MENU\n----\nBREAKFAST");
		printMenu(pancakeIterator);
		System.out.println("\nLUNCH");
		printMenu(dinerIterator);
		System.out.println("\nDINNER");
		printMenu(cafeIterator);
	}
 
	private void printMenu(Iterator iterator) {
		while (iterator.hasNext()) {
			MenuItem menuItem = (MenuItem)iterator.next();
			System.out.print(menuItem.getName() + ", ");
			System.out.print(menuItem.getPrice() + " -- ");
			System.out.println(menuItem.getDescription());
		}
	}
 
	public void printVegetarianMenu() {
		System.out.println("\nVEGETARIAN MENU\n---------------");
		printVegetarianMenu(pancakeHouseMenu.createIterator());
		printVegetarianMenu(dinerMenu.createIterator());
		printVegetarianMenu(cafeMenu.createIterator());
	}
 
	public boolean isItemVegetarian(String name) {
		Iterator pancakeIterator = pancakeHouseMenu.createIterator();
		if (isVegetarian(name, pancakeIterator)) {
			return true;
		}
		Iterator dinerIterator = dinerMenu.createIterator();
		if (isVegetarian(name, dinerIterator)) {
			return true;
		}
		Iterator cafeIterator = cafeMenu.createIterator();
		if (isVegetarian(name, cafeIterator)) {
			return true;
		}
		return false;
	}


	private void printVegetarianMenu(Iterator iterator) {
		while (iterator.hasNext()) {
			MenuItem menuItem = (MenuItem)iterator.next();
			if (menuItem.isVegetarian()) {
				System.out.print(menuItem.getName() + ", ");
				System.out.print(menuItem.getPrice() + " -- ");
				System.out.println(menuItem.getDescription());
			}
		}
	}

	private boolean isVegetarian(String name, Iterator iterator) {
		while (iterator.hasNext()) {
			MenuItem menuItem = (MenuItem)iterator.next();
			if (menuItem.getName().equals(name)) {
				if (menuItem.isVegetarian()) {
					return true;
				}
			}
		}
		return false;
	}
}

Runner

import java.util.*;

public class MenuTestDrive {
	public static void main(String args[]) {
		PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
		DinerMenu dinerMenu = new DinerMenu();
		CafeMenu cafeMenu = new CafeMenu();
 
		Waitress waitress = new Waitress(pancakeHouseMenu, dinerMenu, cafeMenu);
 
		waitress.printMenu();
		waitress.printVegetarianMenu();

		System.out.println("\nCustomer asks, is the Hotdog vegetarian?");
		System.out.print("Waitress says: ");
		if (waitress.isItemVegetarian("Hotdog")) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
		System.out.println("\nCustomer asks, are the Waffles vegetarian?");
		System.out.print("Waitress says: ");
		if (waitress.isItemVegetarian("Waffles")) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
	}
}