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Executors 有个常用静态方法newFixedThreadPool(int nThreads)，来构造线程池
今天我们其源码实现，探一探究竟

//new LinkedBlockingQueue<Runnable>()这里可以看出 是声明的无界队列大小，默认大小为Integer.MAX_VALUE
   public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }

点进去看其实现
corePoolSize、maximumPoolSize 两个值设置为一样，keepAliveTime为空闲线程存活时间，when the number of threads is greater than the core,这里该值为0

//Executors.defaultThreadFactory() 用来构造线程的 Returns a default thread factory used to create new threads.
//defaultHandler: the default rejected execution handler,
//A handler for rejected tasks that throws a RejectedExecutionException 当 Runnable task处理不过来时会派上用场

//private static final RejectedExecutionHandler defaultHandler = new AbortPolicy();

public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
    }

再看下一步调用

    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

至此调用完成。

总结：

• newFixedThreadPool 提供一种快速构造线程池的接口，里面设置了很多默认参数，最终还是调用
  ThreadPoolExecutor来构造 ExecutorService，ThreadPoolExecutor本身是
  ExecutorService接口类的实现类。

• 当默认参数不满足需要是，直接 使用 ThreadPoolExecutor进行构造线程池