设计模式——组合模式

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

实例： 组合菜单和菜单项。

类图：

以下程序演示了打印菜单项和包含菜单项的菜单组合功能。


1.菜单组件抽象类

package net.dp.composite.menu;  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();    }}

2.菜单组

package net.dp.composite.menu; import java.util.Iterator;import java.util.ArrayList; public class Menu extends MenuComponent {    ArrayList<MenuComponent> menuComponents = new ArrayList<MenuComponent>();    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<MenuComponent> iterator = menuComponents.iterator();        while (iterator.hasNext()) {            MenuComponent menuComponent = iterator.next();            menuComponent.print();        }    }}

3.菜单项

package net.dp.composite.menu; public 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());    }}

4.客户端

package net.dp.composite.menu;   public class Waitress {    MenuComponent allMenus;      public Waitress(MenuComponent allMenus) {        this.allMenus = allMenus;    }      public void printMenu() {        allMenus.print();    }}

5.测试

package net.dp.composite.menu; 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();    }}

这样就可以对树形结构中的叶子节点和非叶子节点使用同样的处理方式进行处理。