策略模式

简介

行为型模式，根据不同的情况选择不同的算法策略。Context：上下文角色，屏蔽高层模块对策略、算法的直接访问。简单的策略算法，可以采用枚举策略写法。

示例

public interface IStrategy {
    void doSomeThing();
}
public class StrategyA implements IStrategy{
    @Override
    public void doSomeThing() {
        System.out.println("Algorithm A do some thing!");
    }
}
public class StrategyB implements IStrategy{
    @Override
    public void doSomeThing() {
        System.out.println("Algorithm B do some thing!");
    }
}
public class StrategyC implements IStrategy{
    @Override
    public void doSomeThing() {
        System.out.println("Algorithm C do some thing!");
    }
}
public class Context {
    private IStrategy strategy;

    public Context(IStrategy strategy){
        this.strategy = strategy;
    }

    public void doSomeThing(){
        strategy.doSomeThing();
    }
}

调用

@Test
public void tt(){
    Context context = new Context(new StrategyA());
    context.doSomeThing();

    context = new Context(new StrategyB());
    context.doSomeThing();

    context = new Context(new StrategyC());
    context.doSomeThing();
}

枚举策略

public enum Strategy {
    A{
        @Override
        public void doSomeThing(){
            System.out.println("Algorithm A do some thing!");
        }
    },
    B{
        @Override
        public void doSomeThing(){
            System.out.println("Algorithm B do some thing!");
        }
    },
    C{
        @Override
        public void doSomeThing(){
            System.out.println("Algorithm C do some thing!");
        }
    };

    public abstract void doSomeThing();
}

调用

@Test
public void tt2(){
    Strategy.A.doSomeThing();
    Strategy.B.doSomeThing();
    Strategy.C.doSomeThing();
}