面试问题Executors有哪些创建线程池的方法

下面四个方法本质上都是调用ThreadPoolExecutor的构造方法：

1：Executors.newSingleThreadExecutor()

2：Executors.newFixedThreadPool(nThreads)

3：Executors.newCachedThreadPool()

4：Executors.newScheduledThreadPool(corePoolSize)

corePoolSize：线程池中保留的线程数量，即使这些线程是处于空闲状态

maximumPoolSize：线程池中可创建的最大线程数量

keepAliveTime：当线程数大于corePoolSize数量时，如果线程空闲，这个线程在这个空闲时间后将会销毁

unit：keepAliveTime时间单位

workQueue：任务队列

1：Executors.newSingleThreadExecutor()创建单线程任务线程池

public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue()));
    }

2：Executors.newFixedThreadPool(nThreads)创建固定数量线程线程池

 public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue());
    }

3：Executors.newCachedThreadPool()创建以默认60秒为空闲时间的缓存线程池，核心线程数为0

public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue());
    }

4：Executors.newScheduledThreadPool(corePoolSize)创建可以控制执行时间的线程池

public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
        return new ScheduledThreadPoolExecutor(corePoolSize);
    }

 public ScheduledThreadPoolExecutor(int corePoolSize) {
        super(corePoolSize, Integer.MAX_VALUE, 0, NANOSECONDS,
              new DelayedWorkQueue());
    }