Effective Java 第二版 中文版 笔记（二十一）用函数对象表示策略

不知所谓的用函数对象表示策略

只是去看了下策略模式：菜鸟教程http://www.runoob.com/design-pattern/strategy-pattern.html

步骤 1

创建一个接口。

public interface Strategy {
   public int doOperation(int num1, int num2);
}

步骤 2

创建实现接口的实体类。

//实体类一
public class OperationAdd implements Strategy{
   @Override
   public int doOperation(int num1, int num2) {
      return num1 + num2;
   }
}


//实体类二
public class OperationSubstract implements Strategy{
   @Override
   public int doOperation(int num1, int num2) {
      return num1 - num2;
   }
}

步骤 3

创建 Context 类。

public class Context {
   private Strategy strategy;
 
   public Context(Strategy strategy){
      this.strategy = strategy;
   }
 
   public int executeStrategy(int num1, int num2){
      return strategy.doOperation(num1, num2);
   }
}

步骤 4

使用 Context 来查看当它改变策略 Strategy 时的行为变化。

public class StrategyPatternDemo {
   public static void main(String[] args) {
      Context context = new Context(new OperationAdd());    
      System.out.println("10 + 5 = " + context.executeStrategy(10, 5));
 
      context = new Context(new OperationSubstract());      
      System.out.println("10 - 5 = " + context.executeStrategy(10, 5));
 
      context = new Context(new OperationMultiply());    
      System.out.println("10 * 5 = " + context.executeStrategy(10, 5));
   }
}