策略模式

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。

 

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

public class AddOperation implements Strategy {
    @Override
    public int operate(int num1, int num2) {
        return num1 + num2;
    }
}

public class MultiplyOperation implements Strategy {
    @Override
    public int operate(int num1, int num2) {
        return num1 * num2;
    }
}

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

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

测试：

public class TestDemo {
    public static void main(String[] args) {
        Context c1 = new Context(new AddOperation());
        System.out.println(c1.execute(2,4));

        Context c2 = new Context(new SubtractOperation());
        System.out.println(c2.execute(2,4));

        Context c3 = new Context(new MultiplyOperation());
        System.out.println(c3.execute(2,4));
    }
}

结果：

 

 能看到，算法的改变因newContext的构造方法不同而改变。 它不在编译时候确定，而是运行时候确定算法。