设计模式之组合模式浅析

/**
 * 
 * 
 * 组合模式: 可以使组合对象形成树形结构，以表现出整体/部分的结构，并提供一致的方法访问整体和局部
 *   组合结构内任意对象称为组件，组件可以是组合，也可以是叶节点
 * 客户可以将对象的集合以及个别的对象一视同仁
 * 
 * 运用了递归迭代的思想
 * 
 * 外部迭代器必须维护它在遍历中的位置，以便外部客户可以通过调用hasNext和next方法来驱动遍历
 * 
 * 组合和叶节点都属于组件，只是两者的角色定位不同而已
 * 组合--拥有一群子元素 
 * 叶节点--无子元素
 * 
 * @author Administrator
 * 
 */

菜单组件

package com.undergrowth.composition;

import java.util.Iterator;

/**
 * 
 * 
 * 组合模式: 可以使组合对象形成树形结构，以表现出整体/部分的结构，并提供一致的方法访问整体和局部
 *   组合结构内任意对象称为组件，组件可以是组合，也可以是叶节点
 * 客户可以将对象的集合以及个别的对象一视同仁
 * 
 * 运用了递归迭代的思想
 * 
 * 外部迭代器必须维护它在遍历中的位置，以便外部客户可以通过调用hasNext和next方法来驱动遍历
 * 
 * 组合和叶节点都属于组件，只是两者的角色定位不同而已
 * 组合--拥有一群子元素 
 * 叶节点--无子元素
 * 
 * @author Administrator
 * 
 */
public abstract class MenuComponent {
	/**
	 * 提供的默认实现 让子元素决定是否重写
	 * 
	 * @param 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 float getPrice() {
		throw new UnsupportedOperationException();
	}

	public String getDescription() {
		throw new UnsupportedOperationException();
	}

	public boolean isVegetarian() {
		throw new UnsupportedOperationException();
	}

	public void print() {
		throw new UnsupportedOperationException();

	}

	public abstract Iterator createIterator();
	
}

组合菜单-可拥有菜单项

package com.undergrowth.composition;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Menu extends MenuComponent {

	List<MenuComponent> menus = new ArrayList<>();
	String name;
	String description;

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

	@Override
	public void add(MenuComponent menuComponent) {
		// TODO Auto-generated method stub
		menus.add(menuComponent);
	}

	@Override
	public void remove(MenuComponent menuComponent) {
		// TODO Auto-generated method stub
		menus.remove(menuComponent);
	}

	@Override
	public MenuComponent getChild(int i) {
		// TODO Auto-generated method stub
		return menus.get(i);
	}

	@Override
	public void print() {
		// TODO Auto-generated method stub
		System.out.println(getName()+","+getDescription());
		System.out.println("===============================");
		Iterator iteratorMenu=menus.iterator();
		//迭代递归打印方式
		while (iteratorMenu.hasNext()) {
			MenuComponent menuComponent = (MenuComponent) iteratorMenu.next();
			menuComponent.print();
		}
		System.out.println("==============================================================");
		
	}

	@Override
	public String getName() {
		// TODO Auto-generated method stub
		return name;
	}

	@Override
	public String getDescription() {
		// TODO Auto-generated method stub
		return description;
	}

	/**
	 * 外部迭代器 使用堆栈记录当前迭代位置
	 */
	@Override
	public Iterator createIterator() {
		// TODO Auto-generated method stub
		return new CompositionIterator(menus.iterator());
	}

}

叶子节点菜单项

package com.undergrowth.composition;

import java.util.Iterator;

public class MenuItem extends MenuComponent {
	String name;
	float price;
	String description;
	boolean vegetarian;
	public MenuItem(String name, float price, String description,
			boolean vegetarian) {
		super();
		this.name = name;
		this.price = price;
		this.description = description;
		this.vegetarian = vegetarian;
	}
	public MenuItem(String name, String description,
			boolean vegetarian, double price) {
		super();
		this.name = name;
		this.price = (float) price;
		this.description = description;
		this.vegetarian = vegetarian;
	}
	@Override
	public String getName() {
		// TODO Auto-generated method stub
		return name;
	}
	@Override
	public float getPrice() {
		// TODO Auto-generated method stub
		return price;
	}
	@Override
	public String getDescription() {
		// TODO Auto-generated method stub
		return description;
	}
	@Override
	public boolean isVegetarian() {
		// TODO Auto-generated method stub
		return vegetarian;
	}
	@Override
	public void print() {
		// TODO Auto-generated method stub
		System.out.println(toString());
	}
	@Override
	public String toString() {
		return "MenuItem [name=" + name + ", price=" + price + ", description="
				+ description + ", vegetarian=" + vegetarian + "]";
	}
	@Override
	public Iterator createIterator() {
		// TODO Auto-generated method stub
		return new NullIterator();
	}
	
	
	
}

组合迭代器使用堆栈记录当前的迭代位置

package com.undergrowth.composition;

import java.util.Iterator;
import java.util.Stack;

/**
 * 外部迭代器 使用堆栈记录当前迭代的元素
 * @author Administrator
 *
 */
public class CompositionIterator implements Iterator {

	//使用堆栈 迭代树形结构
	Stack stack=new Stack<>();
	
	public CompositionIterator(Iterator iterator) {
		// TODO Auto-generated constructor stub
		stack.push(iterator);
	}

	@Override
	public boolean hasNext() {
		// TODO Auto-generated method stub
		//判断堆栈是否为空
		if(stack.empty()){
			return false;
		}else {
			Iterator iterator=(Iterator) stack.peek();
			//判断迭代器是否遍历到最后元素
			if(!iterator.hasNext()){
				stack.pop();
				return hasNext();
			}else {
				return true;
			}
		}
		
	}

	@Override
	public Object next() {
		// TODO Auto-generated method stub
		if(hasNext()){
			Iterator iterator=(Iterator) stack.peek();
			MenuComponent menuComponent=(MenuComponent) iterator.next();
			//如果是菜单的话 入栈 遍历 菜单中的菜单项
			if(menuComponent instanceof Menu)
			{
				stack.push(menuComponent.createIterator());
			}
			return menuComponent;
		}else {
			return null;
		}
		
	}

	@Override
	public void remove() {
		// TODO Auto-generated method stub
		throw new UnsupportedOperationException();
	}

}

空迭代器

package com.undergrowth.composition;

import java.util.Iterator;

public class NullIterator implements Iterator {

	@Override
	public boolean hasNext() {
		// TODO Auto-generated method stub
		return false;
	}

	@Override
	public Object next() {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public void remove() {
		// TODO Auto-generated method stub
      throw new UnsupportedOperationException();
	}

}

服务员操作菜单

package com.undergrowth.composition;

import java.util.Iterator;

public class Waitress {
	
	MenuComponent menuComponent;

	public Waitress(MenuComponent menuComponent) {
		super();
		this.menuComponent = menuComponent;
	}
	
	public void print(){
		menuComponent.print();
	}
	
	/**
	 * 打印菜单中的素菜菜单项
	 */
	public void printVegetarianName(){
		Iterator iteratorAll=menuComponent.createIterator();
		while (iteratorAll.hasNext()) {
			MenuComponent currMenuComponent = (MenuComponent) iteratorAll.next();
			try { 
				//表示是菜单项 并且是素菜
				if(currMenuComponent.isVegetarian()){
					System.out.println(currMenuComponent);
				}
			} catch (Exception e) {
				// TODO: handle exception
				//菜单 会抛出异常
			}
		}
	}
	
}

测试

package com.undergrowth.composition.test;

import static org.junit.Assert.*;

import org.junit.Test;

import com.undergrowth.composition.Menu;
import com.undergrowth.composition.MenuComponent;
import com.undergrowth.composition.MenuItem;
import com.undergrowth.composition.Waitress;

public class MenuComponentTest {

	@Test
	public void test() {
		//构建菜单树
		MenuComponent coffeeMenuComponent=new Menu("咖啡菜单", "各种口味的咖啡");
		MenuComponent dessert=new Menu("甜点菜单", "喝咖啡的时候，还可以来点甜点");
		MenuComponent beverage=new Menu("饮料菜单", "品尝甜点的时候，再来点饮料");
		beverage.add(new MenuItem("柠檬雪碧", 22, "加冰，口感更好", true));
		dessert.add(new MenuItem("酸奶蜂蜜冰淇淋", 57, "口感新颖独特，视觉效果也是一流", true));
		dessert.add(new MenuItem("小粉猪奶黄包", 37, "憨态可掬的小粉猪奶黄包", true));
		dessert.add(beverage);
		coffeeMenuComponent.add(dessert);
		coffeeMenuComponent.add(new MenuItem("拿铁咖啡", 100, "咖啡与牛奶的交融", true));
		coffeeMenuComponent.add(new MenuItem("越南咖啡", 200, "采用纯正的越南咖啡豆", true));
		coffeeMenuComponent.add(new MenuItem("美式咖啡", 80, "清新的风味中不失本香", true));
		
		MenuComponent chineseMenuComponent=new Menu("中国菜菜单", "美味的中国菜");
		chineseMenuComponent.add(new MenuItem("宫保鸡", 45, "宫保鸡丁是川菜的代表菜，由鸡脯肉、干辣椒、花生米炒制而成，香辣好吃", false));
		chineseMenuComponent.add(new MenuItem("糖醋里脊", 78, "糖醋里脊色泽红亮、酸甜可口、外酥里嫩", false));
		chineseMenuComponent.add(new MenuItem("烤鸭", 80, "北京烤鸭，被誉为“天下美味”而驰名中外，它更以色泽红润，肉质细嫩，味道醇厚，肥而不腻的特色而享誉海内外", false));
		
		MenuComponent allmenus=new Menu("根菜单", "所有菜单的入口");
		allmenus.add(coffeeMenuComponent);
		allmenus.add(chineseMenuComponent);
		
		Waitress waitress=new Waitress(allmenus);
		waitress.print();
		System.out.println("


");
		System.out.println("==========================打印素食====================================");
		waitress.printVegetarianName();
		
	}

}

控制台输出

根菜单,所有菜单的入口
===============================
咖啡菜单,各种口味的咖啡
===============================
甜点菜单,喝咖啡的时候，还可以来点甜点
===============================
MenuItem [name=酸奶蜂蜜冰淇淋, price=57.0, description=口感新颖独特，视觉效果也是一流, vegetarian=true]
MenuItem [name=小粉猪奶黄包, price=37.0, description=憨态可掬的小粉猪奶黄包, vegetarian=true]
饮料菜单,品尝甜点的时候，再来点饮料
===============================
MenuItem [name=柠檬雪碧, price=22.0, description=加冰，口感更好, vegetarian=true]
==============================================================
==============================================================
MenuItem [name=拿铁咖啡, price=100.0, description=咖啡与牛奶的交融, vegetarian=true]
MenuItem [name=越南咖啡, price=200.0, description=采用纯正的越南咖啡豆, vegetarian=true]
MenuItem [name=美式咖啡, price=80.0, description=清新的风味中不失本香, vegetarian=true]
==============================================================
中国菜菜单,美味的中国菜
===============================
MenuItem [name=宫保鸡, price=45.0, description=宫保鸡丁是川菜的代表菜，由鸡脯肉、干辣椒、花生米炒制而成，香辣好吃, vegetarian=false]
MenuItem [name=糖醋里脊, price=78.0, description=糖醋里脊色泽红亮、酸甜可口、外酥里嫩, vegetarian=false]
MenuItem [name=烤鸭, price=80.0, description=北京烤鸭，被誉为“天下美味”而驰名中外，它更以色泽红润，肉质细嫩，味道醇厚，肥而不腻的特色而享誉海内外, vegetarian=false]
==============================================================
==============================================================




==========================打印素食====================================
MenuItem [name=酸奶蜂蜜冰淇淋, price=57.0, description=口感新颖独特，视觉效果也是一流, vegetarian=true]
MenuItem [name=小粉猪奶黄包, price=37.0, description=憨态可掬的小粉猪奶黄包, vegetarian=true]
MenuItem [name=柠檬雪碧, price=22.0, description=加冰，口感更好, vegetarian=true]
MenuItem [name=柠檬雪碧, price=22.0, description=加冰，口感更好, vegetarian=true]
MenuItem [name=酸奶蜂蜜冰淇淋, price=57.0, description=口感新颖独特，视觉效果也是一流, vegetarian=true]
MenuItem [name=小粉猪奶黄包, price=37.0, description=憨态可掬的小粉猪奶黄包, vegetarian=true]
MenuItem [name=柠檬雪碧, price=22.0, description=加冰，口感更好, vegetarian=true]
MenuItem [name=柠檬雪碧, price=22.0, description=加冰，口感更好, vegetarian=true]
MenuItem [name=柠檬雪碧, price=22.0, description=加冰，口感更好, vegetarian=true]
MenuItem [name=拿铁咖啡, price=100.0, description=咖啡与牛奶的交融, vegetarian=true]
MenuItem [name=越南咖啡, price=200.0, description=采用纯正的越南咖啡豆, vegetarian=true]
MenuItem [name=美式咖啡, price=80.0, description=清新的风味中不失本香, vegetarian=true]

其实在打印素食菜单项的时候会发现有些菜单项重复打印了这是因为采用堆栈进行处理时会产生多级入栈与出栈导致的自己动手画画啊或者调试一下就清楚了

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原文地址：https://www.cnblogs.com/liangxinzhi/p/4275538.html