public class Drop {
  //Message sent from producer to consumer.
  private String message;
  //True if consumer should wait for producer to send message, false
  //if producer should wait for consumer to retrieve message.
  private boolean empty = true;

  public synchronized String take() {
    //Wait until message is available.
    while (empty) {
      try {
        wait();
      } catch (InterruptedException e) {}
    }
    //Toggle status.
    empty = true;
    //Notify producer that status has changed.
    notifyAll();
    return message;
  }

  public synchronized void put(String message) {
    //Wait until message has been retrieved.
    while (!empty) {
      try { 
        wait();
      } catch (InterruptedException e) {}
    }
    //Toggle status.
    empty = false;
    //Store message.
    this.message = message;
    //Notify consumer that status has changed.
    notifyAll();
  }
}