ThreadPoolExecutor executor1 = (ThreadPoolExecutor)Executors.newCachedThreadPool();

ThreadPoolExecutor executor2 = (ThreadPoolExecutor)Executors.newFixedThreadPool(4);

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

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

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

public class Task implements Callable<String> {

private String name;
public Task(String name) {
  this.name = name;
}
@Override
public String call() throws Exception {
  System.out.printf("%s: Starting at : %s\n", this.name, new Date());
  return "hello, world";
}
public static void main(String[] args) {
  ThreadPoolExecutor executor = (ThreadPoolExecutor)Executors.newCachedThreadPool();
  Task task = new Task("test");
  Future<String> result = executor.submit(task);
  try {
    System.out.printf("%s\n", result.get());
  } catch (InterruptedException | ExecutionException e) {
    e.printStackTrace();
  }
  executor.shutdown();
  System.out.printf("Main ends at : %s\n", new Date());
}
}

public void execute(Runnable command) {
  if (command == null)
    throw new NullPointerException();
  int c = ctl.get();
  if (workerCountOf(c) < corePoolSize) {
    if (addWorker(command, true))
      return;
    c = ctl.get();
  }
  if (isRunning(c) && workQueue.offer(command)) {
    int recheck = ctl.get();
    if (! isRunning(recheck) && remove(command))
      reject(command);
    else if (workerCountOf(recheck) == 0)
      addWorker(null, false);
  }
  else if (!addWorker(command, false))
    reject(command);
}

final void runWorker(Worker w) {
  Thread wt = Thread.currentThread();
  Runnable task = w.firstTask;
  w.firstTask = null;
  w.unlock(); // allow interrupts
  boolean completedAbruptly = true;
  try {
    while (task != null || (task = getTask()) != null) {
      w.lock();
  /***/
      try {
        beforeExecute(wt, task);
        Throwable thrown = null;
        try {
          task.run();
        /***/
        } finally {
          afterExecute(task, thrown);
        }
      } finally {
        task = null;
        w.completedTasks++;
        w.unlock();
      }
    }
    completedAbruptly = false;
  } finally {
    processWorkerExit(w, completedAbruptly);
  }
}