策略模式

定义

In computer programming, the strategy pattern (also known as the policy pattern) is a behavioral software design pattern that enables selecting an algorithm at runtime. Instead of implementing a single algorithm directly, code receives run-time instructions as to which in a family of algorithms to use.

场景就是在有多个算法的场景下。

例子

这个模式在框架中非常常见，一个典型场景就是在使用线程池的时候：

    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler)

最后一个参数RejectedExecutionHandler就是个策略模式，拒绝策略。

Context is a class which uses a Strategy.

Context是个具体的类，上例中，ThreadPoolExecutor就是个context。

参考

wiki Strategy_pattern tutorialspoint stategy