public ThreadPoolExecutor(int corePoolSize, //线程池核心工作线程数量，比如newFixedThreadPool中可以自定义的线程数量就是这个参数
                              int maximumPoolSize, //线程池所有工作线程的数量，比如newFixedThreadPool中的最大工作线程就是核心线程数，newCachedThreadPool中的最大工作线程数是Integer.MAX_VALUE
                              long keepAliveTime, //非核心线程存活的时间，当核心线程不够用的时候，创建出来的辅助工作线程在完成任务空闲多久后会被回收
                              TimeUnit unit, //上面一个参数的单位，分。秒等
                              BlockingQueue<Runnable> workQueue,//底层使用的阻塞队列数据结构，比如newFixedThreadPool底层使用LinkedBlockingQueue。工作队列，保存已提交但是未执行的任务
                              ThreadFactory threadFactory, //创建工作线程的工厂，保持默认即可
                              RejectedExecutionHandler handler) { //拒绝策略，即在所有工作线程数达到上限，底层阻塞队列也满了的时候采取的策略
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }