线程池总结

创建方式:

1. ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler);

2. Executors工具类创建：

　　eg:Executors.newFixedThreadPool(nThreads);

工作队列workQueue：

1. ArrayBlockingQueue(size):无序

2. LinkedBlockingQueue(size):有序

3. SynchronousQueue(size):不存储任务，Executors.newCacheThreadPool()用的就是它

拒绝策略handler：

1. AbortPolicy

2. CallerRunsPolicy

3. DiscardPolicy

4. DiscardOldestPolicy