1. 應用場景

這種組合模式正是應樹形結構而生，所以組合模式的使用場景就是出現樹形結構的地方。比如：檔案目錄顯示，多及目錄呈現等樹形結構資料的操作。

2. 概念

將物件組合成樹形結構來表示“整體/部分”層次關係，允許使用者以相同的方式處理單獨物件和組合物件。

3. Class Diagram

元件（Component）類是組合類（Composite）和葉子類（Leaf）的父類，可以把組合類看成是樹的中間節點。

組合物件擁有一個或者多個元件物件，因此組合物件的操作可以委託給元件物件去處理，而元件物件可以是另一個組合物件或者葉子物件。

4. Implementation

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();
    }

    public Iterator createIterator(){
        throw new UnsupportedOperationException();
    }
}

public class Menu extends MenuComponent {
    private ArrayList<MenuComponent> menuComponents=new ArrayList<>();
    private String name;
    private String description;

    public Menu(String name, String description) {
        this.name = name;
        this.description = description;
    }

    @Override
    public void add(MenuComponent menuComponent) {
        menuComponents.add(menuComponent);
    }

    @Override
    public void remove(MenuComponent menuComponent) {
        menuComponents.remove(menuComponent);
    }

    @Override
    public MenuComponent getChild(int i) {
        return menuComponents.get(i);
    }

    @Override
    public String getName() {
        return name;
    }

    @Override
    public String getDescription() {
        return description;
    }

    @Override
    public double getPrice() {
        return super.getPrice();
    }

    @Override
    public void print() {
        System.out.print("\n" + getName());
        System.out.println(", " + getDescription());
        System.out.println("---------------------");

        Iterator<MenuComponent> iterator = menuComponents.iterator();
        while (iterator.hasNext()) {
            MenuComponent menuComponent = iterator.next();
            menuComponent.print();
        }
    }
}

public class MenuItem extends MenuComponent {
    private String name;
    private String decription;
    private boolean vegetarian;
    private double price;

    public MenuItem(String name, String decription, boolean vegetarian, double price) {
        this.name = name;
        this.decription = decription;
        this.vegetarian = vegetarian;
        this.price = price;
    }

    @Override
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String getDescription() {
        return decription;
    }

    @Override
    public boolean isVegetarian() {
        return vegetarian;
    }

    public void setVegetarian(boolean vegetarian) {
        this.vegetarian = vegetarian;
    }

    @Override
    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public void print() {
        System.out.print("  " + getName());
        if (isVegetarian()) {
            System.out.print("(v)");
        }
        System.out.println(", " + getPrice());
        System.out.println("     -- " + getDescription());
    }
}

public class Waitress {
    private MenuComponent menuComponent;

    public Waitress(MenuComponent menuComponent) {
        this.menuComponent = menuComponent;
    }

    public void printMenu(){
        menuComponent.print();
    }
}

public class MenuTestDrive {
	public static void main(String args[]) {
		MenuComponent pancakeHouseMenu = 
			new Menu("PANCAKE HOUSE MENU", "Breakfast");
		MenuComponent dinerMenu = 
			new Menu("DINER MENU", "Lunch");
		MenuComponent cafeMenu = 
			new Menu("CAFE MENU", "Dinner");
		MenuComponent dessertMenu = 
			new Menu("DESSERT MENU", "Dessert of course!");
		MenuComponent coffeeMenu = new Menu("COFFEE MENU", "Stuff to go with your afternoon coffee");
  
		MenuComponent allMenus = new Menu("ALL MENUS", "All menus combined");
  
		allMenus.add(pancakeHouseMenu);
		allMenus.add(dinerMenu);
		allMenus.add(cafeMenu);
  
		pancakeHouseMenu.add(new MenuItem(
			"K&B's Pancake Breakfast", 
			"Pancakes with scrambled eggs, and toast", 
			true,
			2.99));
		pancakeHouseMenu.add(new MenuItem(
			"Regular Pancake Breakfast", 
			"Pancakes with fried eggs, sausage", 
			false,
			2.99));
		pancakeHouseMenu.add(new MenuItem(
			"Blueberry Pancakes",
			"Pancakes made with fresh blueberries, and blueberry syrup",
			true,
			3.49));
		pancakeHouseMenu.add(new MenuItem(
			"Waffles",
			"Waffles, with your choice of blueberries or strawberries",
			true,
			3.59));

		dinerMenu.add(new MenuItem(
			"Vegetarian BLT",
			"(Fakin') Bacon with lettuce & tomato on whole wheat", 
			true, 
			2.99));
		dinerMenu.add(new MenuItem(
			"BLT",
			"Bacon with lettuce & tomato on whole wheat", 
			false, 
			2.99));
		dinerMenu.add(new MenuItem(
			"Soup of the day",
			"A bowl of the soup of the day, with a side of potato salad", 
			false, 
			3.29));
		dinerMenu.add(new MenuItem(
			"Hotdog",
			"A hot dog, with saurkraut, relish, onions, topped with cheese",
			false, 
			3.05));
		dinerMenu.add(new MenuItem(
			"Steamed Veggies and Brown Rice",
			"Steamed vegetables over brown rice", 
			true, 
			3.99));
 
		dinerMenu.add(new MenuItem(
			"Pasta",
			"Spaghetti with Marinara Sauce, and a slice of sourdough bread",
			true, 
			3.89));
   
		dinerMenu.add(dessertMenu);
  
		dessertMenu.add(new MenuItem(
			"Apple Pie",
			"Apple pie with a flakey crust, topped with vanilla icecream",
			true,
			1.59));
  
		dessertMenu.add(new MenuItem(
			"Cheesecake",
			"Creamy New York cheesecake, with a chocolate graham crust",
			true,
			1.99));
		dessertMenu.add(new MenuItem(
			"Sorbet",
			"A scoop of raspberry and a scoop of lime",
			true,
			1.89));

		cafeMenu.add(new MenuItem(
			"Veggie Burger and Air Fries",
			"Veggie burger on a whole wheat bun, lettuce, tomato, and fries",
			true, 
			3.99));
		cafeMenu.add(new MenuItem(
			"Soup of the day",
			"A cup of the soup of the day, with a side salad",
			false, 
			3.69));
		cafeMenu.add(new MenuItem(
			"Burrito",
			"A large burrito, with whole pinto beans, salsa, guacamole",
			true, 
			4.29));

		cafeMenu.add(coffeeMenu);

		coffeeMenu.add(new MenuItem(
			"Coffee Cake",
			"Crumbly cake topped with cinnamon and walnuts",
			true,
			1.59));
		coffeeMenu.add(new MenuItem(
			"Bagel",
			"Flavors include sesame, poppyseed, cinnamon raisin, pumpkin",
			false,
			0.69));
		coffeeMenu.add(new MenuItem(
			"Biscotti",
			"Three almond or hazelnut biscotti cookies",
			true,
			0.89));
 
		Waitress waitress = new Waitress(allMenus);
   
		waitress.printMenu();
	}
}

5. JDK

• javax.swing.JComponent#add(Component)
• java.awt.Container#add(Component)
• java.util.Map#putAll(Map)
• java.util.List#addAll(Collection)
• java.util.Set#addAll(Collection)