策略模式(Strategy)

一.策略模式定义

定义一系列算法，把他们封装起来，并且他们可以相互替换。本模式使得算法可独立于使用他的客户而变化

二.策略模式结构说明

1.Strategy ：策略接口，用来约束一系列具体的策略算法。Context使用这个接口来调用具体的策略实现定义的算法。

2.ConcreteStrategy：具体的策略实现，也就是具体的算法实现。

3.Context：上下文，负责和具体的策略类交互。通常上下文会持有一个真正的策略实现，上下文还可以让具体的策略类来获取上下文的数据，甚至可以让具体的策略类来回调上下文的方法。

三.策略模式的示例代码

package com.interfaces;//策略接口public interface Strategy {double arithmeticInterface();}

package com.model;import com.interfaces.Strategy;//负责和策略接口交互的上下文类public class Context {private Strategy strategy=null;public Context(Strategy strategy) {super();this.strategy = strategy;}public double  quote(){//能实现调用不同的算法return strategy.arithmeticInterface();} }

package com.model;import com.interfaces.Strategy;public class ConcreteStrategy implements Strategy {@Overridepublic double arithmeticInterface() {//具体的算法实现return 0.0;}}

四.策略模式的实例应用--商场价格打折

/** * @author 紫竹 * @function 策略模式实例 * 演示商场打折：  a.对于普通客户或者是新客户报全价 *   b.对于老客户报的价格，统一折扣5% *   c.对于大客户报的价格，统一折扣10% */package com.model;import com.interfaces.Strategy;//计算价格类public class Price {private Strategy strategy=null;public Price(){}public Price(Strategy strategy) {super();this.strategy = strategy;}//根据不同的具体实现的策略，得到不同的价格public double getCustomPrice(double goodsPrice){return strategy.discountPrice(goodsPrice);}public Strategy getStrategy() {return strategy;}public void setStrategy(Strategy strategy) {this.strategy = strategy;}}

package com.interfaces;public interface Strategy {double discountPrice(double goodsPrice);}

package com.model;import com.interfaces.Strategy;//大客户打折的策略具体实现public class LargeCustomStrategy implements Strategy {@Overridepublic double discountPrice(double goodsPrice) {return goodsPrice*(1-0.1);}}

package com.model;import com.interfaces.Strategy;//老客户打折的策略具体实现public class OldCustomStrategy implements Strategy {@Overridepublic double discountPrice(double goodsPrice) {return goodsPrice*(1-0.05);}}

package com.test;import com.model.*;import com.model.Price;//客户端测试public class Client {public static void main(String args[]){double goodsPrice=302.23;Price price=new Price(new LargeCustomStrategy());System.out.println("大客户购买商品的价格为："+price.getCustomPrice(goodsPrice));//不需要修改原来的Price 和 Strategy组合，只需要增加具体的策略即可，正好符合 开-闭的原则price.setStrategy(new OldCustomStrategy());System.out.println("老客户购买商品的价格为："+price.getCustomPrice(goodsPrice));}}

输出结果：

大客户购买商品的价格为：272.007
老客户购买商品的价格为：287.1185

五.模拟JDK中的策略模式实现(comparable&comparator接口)

package com.interfaces;//comparable接口public interface Comparable {int compareTo(Object obj);}

package com.interfaces;//comparator接口public interface Comparator {int compare(Object obj1,Object o2);}

package com.exercise.model;import com.interfaces.Comparable;import com.interfaces.Comparator;//猫类，实现了Comparable接口public class Cat implements Comparable{private int height;private int weight;private Comparator comparator=new CatWeightComparator();public Cat(int height,int weight) {super();this.height = height;this.weight=weight;}public void setHeight(int height) {this.height = height;}public int getHeight() {return height;}public int getWeight() {return weight;}public void setWeight(int weight) {this.weight = weight;}public Comparator getComparator() {return comparator;}public void setComparator(Comparator comparator) {this.comparator = comparator;}@Overridepublic String toString(){return this.getWeight()+"|"+this.getWeight();}@Overridepublic int compareTo(Object obj) {return comparator.compare(this, obj);//使用我指定的方式比较}}

package com.exercise.model;import com.interfaces.Comparator;//猫高度的比较器，比较器的具体实现public class CatHeightComparator implements Comparator{@Overridepublic int compare(Object obj1, Object obj2) {Cat c1=(Cat)obj1;Cat c2=(Cat)obj2;if(c1.getWeight()>c2.getWeight())return 1;else if(c1.getWeight()<c2.getWeight())return -1;else return 0;}}

package com.exercise.model;import com.interfaces.Comparator;//猫重量的比较器public class CatWeightComparator implements Comparator{@Overridepublic int compare(Object obj1, Object obj2) {Cat c1=(Cat)obj1;Cat c2=(Cat)obj2;if(c1.getWeight()>c2.getWeight())return 1;else if(c1.getWeight()<c2.getWeight())return -1;else return 0;}}

package com.exercise.model;import com.interfaces.Comparable;//数据排序public class DataSort{//冒泡排序，整数排序public static void sort(int [] a) {for(int i=0;i<a.length-1;i++){for(int j=0;j<a.length-i-1;j++){if(a[j]>a[j+1]){swap(a,j,j+1);}}}}//交换private static void swap(int[] a, int j, int i) {int temp=a[j];a[j]=a[j+1];a[j+1]=temp;}public static void show(int [] a){for(int value:a){System.out.print(value+"\t");}}//冒泡排序，使用comparable接口实现对任意对象排序(这个对象必须实现Comparable接口)public static void sort(Object [] a) {for(int i=0;i<a.length-1;i++){for(int j=0;j<a.length-i-1;j++){if(((Comparable)a[j]).compareTo((Comparable)a[j+1])==1){//大于swap(a,j,j+1);}}}}//交换private static void swap(Object[] a, int j, int i) {Object temp=a[j];a[j]=a[j+1];a[j+1]=temp;}//显示public static void show(Object [] a){for(Object value:a){System.out.print(value+"\t");}}}

package com.exercise.test;import com.exercise.model.Cat;import com.exercise.model.DataSort;//测试类public class Test {public static void main(String[] args) {//int []a ={3,2,1,45,32,6};Cat cat[]={new Cat(2,2),new Cat(3,3),new Cat(8,8),new Cat(5,5),new Cat(4,4)};DataSort.sort(cat);DataSort.show(cat);}}

输出结果：

2|2 3|3 4|4 5|5 8|8

本文参考了《研磨设计模式》一书，以及马士兵老师的视频，特此声明！