设计模式-组合模式

当有数个对象的集合，它们彼此之间有“整体/部分”的关系，并且你想用一致的方法对待这些对象，就需要用到组合模式。

public abstract class MenuComponent {

	public void add(MenuComponent menuComponent) {
		throw new UnsupportedOperationException();
	}
	
	public void remove(MenuComponent menuComponent) {
		throw new UnsupportedOperationException();
	}
	
	public MenuComponent getChild(int i) {
		throw new UnsupportedOperationException();
	}
	
	public String getName() {
		throw new UnsupportedOperationException();
	}
	
	public String getDescription() {
		throw new UnsupportedOperationException();
	}
	
	public double getPrice() {
		throw new UnsupportedOperationException();
	}
	
	public boolean isVegetarian() {
		throw new UnsupportedOperationException();
	}
	
	public void print() {
		throw new UnsupportedOperationException();
	}
	
	abstract Iterator createIterator();
}

public class Menu extends MenuComponent {

	ArrayList menuComponents = new ArrayList();
	String name;
	String description;
	
	public Menu(String name, String description) {
		super();
		this.name = name;
		this.description = description;
	}
	
	@Override
	public void add(MenuComponent component) {
		menuComponents.add(component);
	}
	
	@Override
	public void remove(MenuComponent component) {
		menuComponents.remove(component);
	}
	
	@Override
	public MenuComponent getChild(int i) {
		return (MenuComponent) menuComponents.get(i);
	}
	
	@Override
	public String getName() {
		return name;
	}
	
	@Override
	public String getDescription() {
		return description;
	}
	
	@Override
	public void print() {
		System.out.print("\n" + getName());
		System.out.println(", " + getDescription());
		System.out.println("-----------------------");
		
		Iterator iterator = menuComponents.iterator();
		while (iterator.hasNext()) {
			MenuComponent component = (MenuComponent) iterator.next();
			component.print();
		}
	}

	@Override
	Iterator createIterator() {
		return new CompositeIterator(menuComponents.iterator());
	}
}

public class MenuItem extends MenuComponent {
	String name;
	String description;
	boolean vegetarian;
	double price;
	
	public MenuItem(String name, String description, boolean vegetarian,
			double price) {
		super();
		this.name = name;
		this.description = description;
		this.vegetarian = vegetarian;
		this.price = price;
	}
	
	@Override
	public String getName() {
		return name;
	}
	
	@Override
	public String getDescription() {
		return description;
	}
	
	@Override
	public double getPrice() {
		return price;
	}
	
	@Override
	public boolean isVegetarian() {
		return vegetarian;
	}
	
	public void print() {
		System.out.print(" " + getName());
		if (isVegetarian()) {
			System.out.println("(v)");
		}
		System.out.println(", " + getPrice());
		System.out.println("   --" + getDescription());
	}

	@Override
	Iterator createIterator() {
		return new NullIterator();
	}
}

public class CompositeIterator implements Iterator {

	Stack<Iterator> stack = new Stack<Iterator>();
	
	public CompositeIterator(Iterator iterator) {
		stack.add(iterator);
	}
	
	@Override
	public boolean hasNext() {
		if (stack.empty()) {
			return false;
		} else {
			Iterator iterator = stack.peek();
			if (!iterator.hasNext()) {
				stack.pop();
				return hasNext();
			} else 
				return true;
		}
	}

	@Override
	public Object next() {
		if (hasNext()) {
			Iterator iterator = stack.peek();
			MenuComponent component = (MenuComponent) iterator.next();
			if (component instanceof Menu) {
				stack.push(component.createIterator());
			}
			return component;
		} else 
			return null;
	}

	@Override
	public void remove() {
		throw new UnsupportedOperationException();
	}

}

public class NullIterator implements Iterator {

	@Override
	public boolean hasNext() {
		return false;
	}

	@Override
	public Object next() {
		return null;
	}

	@Override
	public void remove() {
		throw new UnsupportedOperationException();
	}

}

public class Waitress {

	MenuComponent allMenus;
	
	public Waitress(MenuComponent allMenus) {
		this.allMenus = allMenus;
	}
	
	public void printMenu() {
		this.allMenus.print();
	}
	
	public void printVegetarianMenu() {
		Iterator iterator = allMenus.createIterator();
		
		while (iterator.hasNext()) {
			MenuComponent component = (MenuComponent) iterator.next();
			try {
				if (component.isVegetarian()) {
					component.print();
				}
			} catch (UnsupportedOperationException e) {
				e.printStackTrace();
			}
		}
	}
}

public class MenuTestDrive {

	public static void main(String[] args) {

		MenuComponent pancakeHouseMenu = 
				new Menu("PANCAKE HOUSE MENU", "Breakfase");
		MenuComponent dinerMenu = 
				new Menu("DINER MENU", "Lunch");
		MenuComponent cafeMenu = 
				new Menu("CAFE", "Dinner");
		MenuComponent dessertMenu = 
				new Menu("DESSERT MENU", "Dessert of course!");
		
		MenuComponent allMenus = 
				new Menu("ALL MENUS" , "ALL menus combined");
		
		allMenus.add(pancakeHouseMenu);
		allMenus.add(dinerMenu);
		allMenus.add(cafeMenu);
		
		dinerMenu.add(new MenuItem("Pasta", "Spaghetti with Marinara Sauce", true, 3.89));
		dinerMenu.add(dessertMenu);
		dessertMenu.add(new MenuItem("Apple Pie", "Apple pie with a flakey crust", true, 1.99));
		
		Waitress waitress = new Waitress(allMenus);
		waitress.printMenu();
		
	}

}