策略模式

一个类的行为或其算法可以在运行期更改。众多算法相似的时候，使用if else引发过于复杂难以维护。

策略接口：

public interface Strategy {

    int operation(int a, int b);
}

不同的策略：

public class OperationAdd implements Strategy {

    @Override
    public int operation(int a, int b) {
        return a + b;
    }
}

public class OperationSub implements Strategy {

    @Override
    public int operation(int a, int b) {
        return a - b;
    }
}

持有策略的上下文：

public class Context {

    private Strategy strategy;

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

    public int executeStrategy(int a, int b) {
        return strategy.operation(a, b);
    }
}

测试类：

public class Main {

    public static void main(String[] args) {
        Context context = new Context(new OperationAdd());
        System.out.println(context.executeStrategy(1, 2));

        context = new Context(new OperationSub());
        System.out.println(context.executeStrategy(5, 3));
    }
}