boolean success = q.offer(x,100,TimeUnit.MILLISECONDS);

Object head = q.poll(100, TimeUnit.MILLISECONDS);

public interface Delayed extends Comparable<Delayed> { 
   long getDelay(TimeUnit unit); 
} 

public class BlockingQueueTest { 
  public static void main(String[] args) { 
    Scanner in = new Scanner(System.in); 
    System.out.print("Enter base directory (e.g. /usr/local/jdk5.0/src): "); 
    String directory = in.nextLine(); 
    System.out.print("Enter keyword (e.g. volatile): "); 
    String keyword = in.nextLine(); 
 
    final int FILE_QUEUE_SIZE = 10;// 阻塞队列大小 
    final int SEARCH_THREADS = 100;// 关键字搜索线程个数 
 
    // 基于ArrayBlockingQueue的阻塞队列 
    BlockingQueue<File> queue = new ArrayBlockingQueue<File>( 
        FILE_QUEUE_SIZE); 
 
    //只启动一个线程来搜索目录 
    FileEnumerationTask enumerator = new FileEnumerationTask(queue, 
        new File(directory)); 
    new Thread(enumerator).start(); 
     
    //启动100个线程用来在文件中搜索指定的关键字 
    for (int i = 1; i <= SEARCH_THREADS; i++) 
      new Thread(new SearchTask(queue, keyword)).start(); 
  } 
} 
class FileEnumerationTask implements Runnable { 
  //哑元文件对象，放在阻塞队列最后，用来标示文件已被遍历完 
  public static File DUMMY = new File(""); 
 
  private BlockingQueue<File> queue; 
  private File startingDirectory; 
 
  public FileEnumerationTask(BlockingQueue<File> queue, File startingDirectory) { 
    this.queue = queue; 
    this.startingDirectory = startingDirectory; 
  } 
 
  public void run() { 
    try { 
      enumerate(startingDirectory); 
      queue.put(DUMMY);//执行到这里说明指定的目录下文件已被遍历完 
    } catch (InterruptedException e) { 
    } 
  } 
 
  // 将指定目录下的所有文件以File对象的形式放入阻塞队列中 
  public void enumerate(File directory) throws InterruptedException { 
    File[] files = directory.listFiles(); 
    for (File file : files) { 
      if (file.isDirectory()) 
        enumerate(file); 
      else 
        //将元素放入队尾，如果队列满，则阻塞 
        queue.put(file); 
    } 
  } 
} 
class SearchTask implements Runnable { 
  private BlockingQueue<File> queue; 
  private String keyword; 
 
  public SearchTask(BlockingQueue<File> queue, String keyword) { 
    this.queue = queue; 
    this.keyword = keyword; 
  } 
 
  public void run() { 
    try { 
      boolean done = false; 
      while (!done) { 
        //取出队首元素，如果队列为空，则阻塞 
        File file = queue.take(); 
        if (file == FileEnumerationTask.DUMMY) { 
          //取出来后重新放入，好让其他线程读到它时也很快的结束 
          queue.put(file); 
          done = true; 
        } else 
          search(file); 
      } 
    } catch (IOException e) { 
      e.printStackTrace(); 
    } catch (InterruptedException e) { 
    } 
  } 
  public void search(File file) throws IOException { 
    Scanner in = new Scanner(new FileInputStream(file)); 
    int lineNumber = 0; 
    while (in.hasNextLine()) { 
      lineNumber++; 
      String line = in.nextLine(); 
      if (line.contains(keyword)) 
        System.out.printf("%s:%d:%s%n", file.getPath(), lineNumber, 
            line); 
    } 
    in.close(); 
  } 
}