线程池理解

线程池的构造函数：

1. corePoolSize： the number of threads to keep in the pool, even if they are idle, unless {@code allowCoreThreadTimeOut} is set（线程池中活跃的线程数，即使他们是空闲的，没有任务可以执行的，也不会销毁，除非设置 allowCoreThreadTimeOut）
2. maximumPoolSize： the maximum number of threads to allow in the pool（线程池中允许的最大线程数量）
3. keepAliveTime： when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating.（当线程的数量大于核心线程数的时候，空闲的线程在他们销毁到等待新的任务到来，这段时间的最大值）
4. unit： the time unit for the {@code keepAliveTime} argument（keepAliveTime 的时间单位）
5. workQueue： the queue to use for holding tasks before they are executed. This queue will hold only the {@code Runnable} tasks submitted by the {@code execute} method.（任务执行之前保存任务的队列，该队列将只保存由{@code execute}方法提交的{@code Runnable}任务）
6. threadFactory： the factory to use when the executor creates a new thread（执行程序创建新线程时要使用的工厂）
7. handler：the handler to use when execution is blocked because the thread bounds and queue capacities are reached（当执行因达到线程边界和队列容量而阻塞时要使用的处理程序）