本篇博文说的是组合模式

描述性文字

组合模式，又称为 部分整体模式，把具有相似的一组对象 当做一个对象处理，用一种树状的结构来组合对象，再提供统一的方法去访问相似的对象，以此忽略掉对象与对象容器间的差别。

举个栗子

注：此处直接使用的是原图。

假设这两类需求如下：

菜单：菜单名，描述信息，添加，添加删除子菜单或菜品 递归打印出所有的子菜单与菜品！

菜品：菜名，描述信息，价格，打印信息好的，先试试不用组合模式，要怎么写~

不使用组合模式写菜单

示例代码：

package structPattrn.compositePattern; import java.util.ArrayList; import java.util.List; /** * 组合模式测试例程 * @Package structPattrn.compositePattern * @Title: CompositePatternDemo.java * @Company: $ * @author BurgessLee * @date 2018年10月25日-下午5:06:05 * @Description: $ */ public class CompositePatternDemo { public static void main(String[] args) { //不用组合模式测试例程 Menu menu = new Menu("大菜单","包含所有的子菜单"); Menu drinkMenu = new Menu("饮品菜单","都是喝的"); Menu eatMenu = new Menu("小吃菜单","都是吃的"); MilkTea milkTea = new MilkTea("珍珠卖茶","珍珠+奶茶", 5); Juice juice = new Juice("猕猴桃饮料","无添加剂",5); HandCake handCake = new HandCake("咖喱鱼蛋","微辣",6); FishBoll fishBoll = new FishBoll("培根手抓饼","正宗台湾风味",6); drinkMenu.addMilkTea(milkTea); drinkMenu.addJuice(juice); eatMenu.addHandCake(handCake); eatMenu.addFishBoll(fishBoll); menu.addMenu(drinkMenu); menu.addMenu(eatMenu); System.out.println(menu.toString()); } } //以下部分代码使用的不是组合模式实现的========================================================================== class MilkTea{ private String name; private String desc; private int price; public MilkTea(String name, String desc, int price) { super(); this.name = name; this.desc = desc; this.price = price; } @Override public String toString() { return "MilkTea [name=" + name + ", desc=" + desc + ", price=" + price + "]"; } } class Juice{ private String name; private String desc; private int price; public Juice(String name, String desc, int price) { super(); this.name = name; this.desc = desc; this.price = price; } @Override public String toString() { return "Juice [name=" + name + ", desc=" + desc + ", price=" + price + "]"; } } class HandCake{ private String name; private String desc; private int price; public HandCake(String name, String desc, int price) { super(); this.name = name; this.desc = desc; this.price = price; } @Override public String toString() { return "HandCake [name=" + name + ", desc=" + desc + ", price=" + price + "]"; } } class FishBoll{ private String name; private String desc; private int price; public FishBoll(String name, String desc, int price) { super(); this.name = name; this.desc = desc; this.price = price; } @Override public String toString() { return "FishBoll [name=" + name + ", price=" + price + "]"; } } class Menu{ private String name; private String desc; private List<Menu> menus = new ArrayList<>(); private List<MilkTea> milkTeas = new ArrayList<>(); private List<Juice> juices = new ArrayList<>(); private List<HandCake> handCakes = new ArrayList<>(); private List<FishBoll> fishBolls = new ArrayList<>(); public Menu(String name, String desc) { super(); this.name = name; this.desc = desc; } public void addMilkTea(MilkTea milkTea){ this.milkTeas.add(milkTea); } public void addJuice(Juice juice){ this.juices.add(juice); } public void addHandCake(HandCake handCake){ this.handCakes.add(handCake); } public void addFishBoll(FishBoll fishBoll){ this.fishBolls.add(fishBoll); } public void addMenu(Menu menu){ this.menus.add(menu); } @Override public String toString() { return "Menu [name=" + name + ", desc=" + desc + ", menus=" + menus + ", milkTeas=" + milkTeas + ", juices=" + juices + ", handCakes=" + handCakes + ", fishBolls=" + fishBolls + "]"; } }

打印结果：

Menu [name=大菜单, desc=包含所有的子菜单, menus=[Menu [name=饮品菜单, desc=都是喝的, menus=[], milkTeas=[MilkTea [name=珍珠卖茶, desc=珍珠+奶茶, price=5]], juices=[Juice [name=猕猴桃饮料, desc=无添加剂, price=5]], handCakes=[], fishBolls=[]], Menu [name=小吃菜单, desc=都是吃的, menus=[], milkTeas=[], juices=[], handCakes=[HandCake [name=咖喱鱼蛋, desc=微辣, price=6]], fishBolls=[FishBoll [name=培根手抓饼, price=6]]]], milkTeas=[], juices=[], handCakes=[], fishBolls=[]]

使用组合模式写菜单

示例代码:

abstract class AbstractMenu{ public abstract void add(AbstractMenu menu); public abstract AbstractMenu get(int index); public abstract String getString(); } class MileTeaNew extends AbstractMenu{ private String name; private String desc; private int price; public MileTeaNew(String name, String desc, int i) { super(); this.name = name; this.desc = desc; this.price = i; } @Override public void add(AbstractMenu menu) { /*未使用*/ } @Override public AbstractMenu get(int index) { return null; } @Override public String getString() { return toString(); } @Override public String toString() { return "MileTeaNew [name=" + name + ", desc=" + desc + ", price=" + price + "]"; } } class JuiceNew extends AbstractMenu{ private String name; private String desc; private int price; public JuiceNew(String name, String desc) { super(); this.name = name; this.desc = desc; } @Override public void add(AbstractMenu menu) { /*未使用*/ } @Override public AbstractMenu get(int index) { return null; } @Override public String getString() { return toString(); } @Override public String toString() { return "MileTeaNew [name=" + name + ", desc=" + desc + ", price=" + price + "]"; } } class HandCakeNew extends AbstractMenu{ private String name; private String desc; private int price; public HandCakeNew(String name, String desc) { super(); this.name = name; this.desc = desc; } @Override public void add(AbstractMenu menu) { /*未使用*/ } @Override public AbstractMenu get(int index) { return null; } @Override public String getString() { return toString(); } @Override public String toString() { return "MileTeaNew [name=" + name + ", desc=" + desc + ", price=" + price + "]"; } } class FishBollNew extends AbstractMenu{ private String name; private String desc; private int price; public FishBollNew(String name, String desc) { super(); this.name = name; this.desc = desc; } @Override public void add(AbstractMenu menu) { /*未使用*/ } @Override public AbstractMenu get(int index) { return null; } @Override public String getString() { return toString(); } @Override public String toString() { return "MileTeaNew [name=" + name + ", desc=" + desc + ", price=" + price + "]"; } } class MenuNew extends AbstractMenu{ private String name; private String desc; private List<AbstractMenu> menus = new ArrayList<>(); public MenuNew(String name, String desc) { super(); this.name = name; this.desc = desc; } @Override public void add(AbstractMenu menu) { this.menus.add(menu); } @Override public AbstractMenu get(int index) { return this.menus.get(index); } @Override public String getString() { return toString(); } @Override public String toString() { return "MenuNew [name=" + name + ", desc=" + desc + ", menus=" + menus + "]"; } }

测试例程：

MenuNew menuNew = new MenuNew("大菜单","包含所有的子菜单"); MenuNew drinkMenuNew = new MenuNew("饮品菜单","都是喝的"); MenuNew eatMenuNew = new MenuNew("小吃菜单","都是吃的"); MileTeaNew milkTeaNew = new MileTeaNew("珍珠卖茶","珍珠+奶茶",6); JuiceNew juiceNew = new JuiceNew("猕猴桃饮料","无添加剂"); HandCakeNew handCakeNew = new HandCakeNew("咖喱鱼蛋","微辣"); FishBollNew fishBollNew = new FishBollNew("培根手抓饼","正宗台湾风味"); drinkMenuNew.add(milkTeaNew); drinkMenuNew.add(juiceNew); eatMenuNew.add(handCakeNew); eatMenuNew.add(fishBollNew); menuNew.add(drinkMenuNew); menuNew.add(eatMenuNew); menuNew.getString();

使用了合并模式，如果此时我们要新增一个菜品，只需继承抽象构建类， 无需改动其他类，显得更加方便。

概念与总结

三个角色 上面也说了合并模式是用一种树状的结构来组合对象，三个名词 根节点，枝结点，叶子结点，类比上面那个菜单的图， 根节点是菜单，枝结点是饮料菜单和小吃菜单， 叶子结点是奶茶，果汁，手抓饼和鱼蛋！

Component：抽象组件，为组合中的对象声明接口，让客户端 可以通过这个接口来访问和管理整个对象结构，可以在里面为定义的 功能提供缺省的实现，比如上面的AbstractMenu类。Composite：容器组件，继承抽象组件，实现抽象组件中与 叶子组件相关的操作，比如上面的Menu类重写了get，set方法。此处重写的是toString方法也就是，抽象类中的getString方法Leaf：叶子组件，定义和实现叶子对象的行为，不再包含其它 的子节点对象，比如上面的MilkTea，Juice，HandCakeFishBall。

UML图

使用情景

如果你想表示对象的部分-整体层次结构，可以选用组合模式，把整体和部分的操作统一起来，使得层次结构实现更简单，从外 部来使用这个层次结构也简单；如果你希望统一的使用组合结构中的所有对象，可以选用组合模式，这正是组合模式提供的主要功能；

 

优缺点

优点：

让客户端更加简单，客户端不需要再操心面对的是组合对象还是叶节点对象，所以不需要写一大堆if语句来保证他们对正确的对象调用了正确 的方法。通常，他们只需要对整个结构调用一个方法并执行操作就可以了。

缺点：

容易增加新的组件也会带来一些问题，比如很难限制组合中的组件类型。 这在需要检测组件类型的时候，使得我们不能依靠编译期的类型约束来 完成，必须在运行期间动态检测。