策略模式

简介

在策略模式（Strategy Pattern）中，一个类的行为或其算法可以在运行时更改。这种类型的设计模式属于行为型模式。

在策略模式中，我们创建表示各种策略的对象和一个行为随着策略对象改变而改变的 context 对象。策略对象改变 context 对象的执行算法。

实现

1. 创建一个接口

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

2. 创建实现接口的实体类

public class OperationAdd 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;
    }
}

public class OperationSubtract implements Strategy {
    @Override
    public int doOperation(int num1, int num2) {
        return num1 - num2;
    }
}

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);
    }
}

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 OperationSubtract());
        System.out.println("10 - 5 = " + context.executeStrategy(10, 5));

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

类图

代码

策略模式 (opens new window)