设计模式——行为型模式_策略模式

1. 类图

2. 代码

• 策略相关
  • 策略总接口

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

  • 策略实现类：具体策略

    • public class OperationAdd implements Strategy{
         @Override
         public int doOperation(int num1, int num2) {
            return num1 + num2;
         }
      }
      
      public class OperationSubtract implements Strategy{
         @Override
         public int doOperation(int num1, int num2) {
            return num1 - num2;
         }
      }
      
      public class OperationMultiply implements Strategy{
         @Override
         public int doOperation(int num1, int num2) {
            return num1 * num2;
         }
      }

• Context类（封装策略）

  • 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);
       }
    }

• 客户端调用

  • 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 OperationSubtract());      
          System.out.println("10 - 5 = " + context.executeStrategy(10, 5));
     
          context = new Context(new OperationMultiply());    
          System.out.println("10 * 5 = " + context.executeStrategy(10, 5));
       }
    }

3. 总结

• 优点：
  • 扩展性良好，增加一个策略只需实现接口即可
  • 避免用if else判断
• 缺点：
  • 策略类数量会增多，每个策略都是一个类，复用的可能性很小
  • 所有的策略类都需要对外暴露