结构图：

实现：

1 abstract public class Strategy {2     public void algrithmInterface()3     {    4     }5 }

1 public class StrategyA extends Strategy{ 2  3     @Override 4     public void algrithmInterface() { 5         super.algrithmInterface(); 6         System.out.println("算法A的实现"); 7     } 8      9 10 }

1 public class StrategyB extends Strategy{ 2  3     @Override 4     public void algrithmInterface() { 5         super.algrithmInterface(); 6         System.out.println("算法B的实现"); 7     } 8      9 10 }

1 public class Context { 2  3     private Strategy strategy; 4  5     public Context(Strategy strategy) { 6         super(); 7         this.strategy = strategy; 8     } 9     10     public void contextInterface()11     {12         strategy.algrithmInterface();13     }14     15     public void setStrategy(Strategy s)16     {17         this.strategy = s;18     }19 }

1 public class Client { 2     public static void main(String[] args) 3     { 4         Context context = new Context(new StrategyA()); 5         context.contextInterface(); 6          7         context.setStrategy(new StrategyB()); 8         context.contextInterface(); 9     }10 }

应用常用：

该模式封装了一系列算法，让它们而已相互替换，而不会影响到客户端的变化。