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/jdk1.6.0/src): "); 
      String directory = in.nextLine(); 
      System.out.print("Enter keyword (e.g. volatile): "); 
      String keyword = in.nextLine(); 

      final int FILE_QUEUE_SIZE = 10; 
      final int SEARCH_THREADS = 100; 

      BlockingQueue<File> queue = new ArrayBlockingQueue<File>(FILE_QUEUE_SIZE); 

      FileEnumerationTask enumerator = new FileEnumerationTask(queue, new File(directory)); 
      new Thread(enumerator).start(); 
      for (int i = 1; i <= SEARCH_THREADS; i++) 
         new Thread(new SearchTask(queue, keyword)).start(); 
   } 
} 

/** 
 * This task enumerates all files in a directory and its subdirectories. 
 */
class FileEnumerationTask implements Runnable 
{ 
   /** 
    * Constructs a FileEnumerationTask. 
    * @param queue the blocking queue to which the enumerated files are added 
    * @param startingDirectory the directory in which to start the enumeration 
    */
   public FileEnumerationTask(BlockingQueue<File> queue, File startingDirectory) 
   { 
      this.queue = queue; 
      this.startingDirectory = startingDirectory; 
   } 

   public void run() 
   { 
      try
      { 
         enumerate(startingDirectory); 
         queue.put(DUMMY); 
      } 
      catch (InterruptedException e) 
      { 
      } 
   } 

   /** 
    * Recursively enumerates all files in a given directory and its subdirectories 
    * @param directory the directory in which to start 
    */
   public void enumerate(File directory) throws InterruptedException 
   { 
      File[] files = directory.listFiles(); 
      for (File file : files) 
      { 
         if (file.isDirectory()) enumerate(file); 
         else queue.put(file); 
      } 
   } 

   public static File DUMMY = new File(""); 

   private BlockingQueue<File> queue; 
   private File startingDirectory; 
} 

/** 
 * This task searches files for a given keyword. 
 */
class SearchTask implements Runnable 
{ 
   /** 
    * Constructs a SearchTask. 
    * @param queue the queue from which to take files 
    * @param keyword the keyword to look for 
    */
   public SearchTask(BlockingQueue<File> queue, String keyword) 
   { 
      this.queue = queue; 
      this.keyword = keyword; 
   } 

   public void run() 
   { 
      try
      { 
         boolean done = false; 
         while (!done) 
         { 
            File file = queue.take(); 
            if (file == FileEnumerationTask.DUMMY) 
            { 
               queue.put(file); 
               done = true; 
            } 
            else search(file);             
         } 
      } 
      catch (IOException e) 
      { 
         e.printStackTrace(); 
      } 
      catch (InterruptedException e) 
      { 
      }       
   } 

   /** 
    * Searches a file for a given keyword and prints all matching lines. 
    * @param file the file to search 
    */
   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().trim(); 
         if (line.contains(keyword)) System.out.printf("%s:%d    %s%n", file.getPath(), lineNumber, line); 
      } 
      in.close(); 
   } 

   private BlockingQueue<File> queue; 
   private String keyword; 
}