策略模式Strategy

原创转载请注明出处：https://www.cnblogs.com/agilestyle/p/11400764.html

1. 定义

定义一系列的算法，把它们一个个封装起来，并且使它们可相互替换。本模式使得算法可独立于使用它的客户而变化。

2.结构图

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。
ConcreteStrategy：具体的策略实现，也就是具体的算法实现。
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，甚至让具体的策略类来回调上下文的方法。

3. 本质

策略模式的本质：分离算法，选择实现。

4.Code Demo

Strategy.java

1 package org.fool.dp.strategy;
2 
3 public interface Strategy {
4     int calculate(int a, int b);
5 }

AddStrategy.java

1 package org.fool.dp.strategy;
2 
3 public class AddStrategy implements Strategy {
4     @Override
5     public int calculate(int a, int b) {
6         return a + b;
7     }
8 }

SubtractStrategy.java

1 package org.fool.dp.strategy;
2 
3 public class SubtractStrategy implements Strategy {
4     @Override
5     public int calculate(int a, int b) {
6         return a - b;
7     }
8 }

MultiplyStrategy.java

1 package org.fool.dp.strategy;
2 
3 public class MultiplyStrategy implements Strategy {
4     @Override
5     public int calculate(int a, int b) {
6         return a * b;
7     }
8 }

DivideStrategy.java

1 package org.fool.dp.strategy;
2 
3 public class DivideStrategy implements Strategy {
4     @Override
5     public int calculate(int a, int b) {
6         return a / b;
7     }
8 }

Context.java

 1 package org.fool.dp.strategy;
 2 
 3 public class Context {
 4     private Strategy strategy;
 5 
 6     public Context(Strategy strategy) {
 7         this.strategy = strategy;
 8     }
 9 
10     public int calculate(int a, int b) {
11         return strategy.calculate(a, b);
12     }
13 }

Client.java

 1 package org.fool.dp.strategy;
 2 
 3 public class Client {
 4     public static void main(String[] args) {
 5         Strategy addStrategy = new AddStrategy();
 6         Context context = new Context(addStrategy);
 7         System.out.println(context.calculate(1, 2));
 8 
 9         Strategy subtractStrategy = new SubtractStrategy();
10         context = new Context(subtractStrategy);
11         System.out.println(context.calculate(1, 2));
12 
13         Strategy multiplyStrategy = new MultiplyStrategy();
14         context = new Context(multiplyStrategy);
15         System.out.println(context.calculate(1, 2));
16 
17         Strategy devideStrategy = new DivideStrategy();
18         context = new Context(devideStrategy);
19         System.out.println(context.calculate(1, 2));
20     }
21 }