组合模式允许你将对象组合成树形结构来表现“整体/部分”层次结构。组合能让客户以一致的方式处理个别对象以及对象组合。

类图

（图片源于网络）

代码实现（Java）

// Waitress.javapublic class Waitress {    MenuComponent allMenus;                           public Waitress(MenuComponent allMenus) {        this.allMenus = allMenus;    }                           public void printMenu() {        allMenus.print();    }}

// MenuComponent.javapublic 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();    }}

// MenuItem.javapublic class MenuItem extends MenuComponent {    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 void print() {        System.out.print("  " + getName());        if (isVegetarian()) {            System.out.print("(v)");        }        System.out.println(", " + getPrice());        System.out.println("     -- " + getDescription());    }}

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

测试代码

// MenuTestDrive.javapublic 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();    }}

运行效果