用JAVA实现一个线程池，线程池在初始状态下没有任何工作线程。当工作队列中有未执行的任务时，分一下两种情况处理：
. 如果线程池中工作线程数目为MAX_SIZE，那就什么也不做；
. 如果线程池中工作线程数目小于MAX_SIZE，那么创建一个工作线程，使它执行新任务。
对于线程池中空闲的工作线程，如果其闲置时间超过TIMEOUT秒，就销毁该线程。(A thread pool is implemented with JAVA, and the thread pool has no working thread in the initial state. When there is an un - executed task in a work queue, two cases are dealt with:
If the number of working threads in the thread pool is MAX_SIZE, then nothing will be done.
If the number of working threads in the thread pool is less than MAX_SIZE, then a working thread is created to make it perform a new task.
For the idle working thread in the thread pool, the thread is destroyed if it is idle for more than TIMEOUT seconds.)