How does this thread behave?

Question

CubbyHole class
public class CubbyHole {
     Object item;
     public synchronized Object get()
               throws InterruptedException {
          while(item == null)
               wait();
          Object i = item;
          item = null;
          notifyAll();
          return i;
     public synchronized void put(Object i)
               throws InterruptedException {
          while(item != null)
               wait();
          item = i;
          notifyAll();
}and
TestCubbyHole
public class TestCubbyHole {
     public static void main(String[] args) {
          Thread mainThread = Thread.currentThread();
          CubbyHole c = new CubbyHole();
          new CubbyWatcher(1, c);
          new CubbyWatcher(2, c);
          new CubbyWatcher(3, c);
          new CubbyWatcher(4, c);
          new CubbyWatcher(5, c);
          new CubbyWatcher(6, c);
          for(int ii=0 ; ii<args.length ; ii++) {
               new CubbyFiller(args[ii], c);
          try {
               System.in.read();
          } catch (java.io.IOException ioe) {
     static class CubbyWatcher implements Runnable {
          int id;
          CubbyHole theCubbyHole;
          public CubbyWatcher(int id, CubbyHole c) {
               this.id = id;
               theCubbyHole = c;
               System.out.println("CubbyWatcher");
               Thread t = new Thread(this);
               t.setDaemon(true);
               t.start();
          public void run() {
               while(true) {
                    try {
                         Object o = theCubbyHole.get();
                         System.out.println("Watcher #" + id +
                                   " got: " + o);
                    } catch (InterruptedException ie) {
     static class CubbyFiller implements Runnable {
          Object item;
          CubbyHole theCubbyHole;
          public CubbyFiller(Object i, CubbyHole c) {
               item = i;
               theCubbyHole = c;
               System.out.println("CubbyFiller" + ", item = " + item);
               Thread t = new Thread(this);
               t.setDaemon(true);
               t.start();
          public void run() {
               Thread me = Thread.currentThread();
               //int waitTime = (int)(Math.random() * 1000);
               try {
                    //me.sleep(waitTime);
                    theCubbyHole.put(item);
               } catch (InterruptedException ie) {
}In TestCubbyHole's CubbyFiller's run() method, if let the me.sleep uncommented, the output will be something like
parameter: aaa bbb ccc ddd eee
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyFiller, item = aaa
CubbyFiller, item = bbb
CubbyFiller, item = ccc
CubbyFiller, item = ddd
CubbyFiller, item = eee
Watcher #1 got: ddd
Watcher #2 got: ccc
Watcher #3 got: bbb
Watcher #4 got: aaa
Watcher #5 got: eee
where the last 4 lines (Watcher #s) are quite random. I understand that.
However, if with the code lines commented, I expect the out put to be:
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyFiller, item = aaa
CubbyFiller, item = bbb
CubbyFiller, item = ccc
CubbyFiller, item = ddd
CubbyFiller, item = eee
Watcher #1 got: aaa
Watcher #2 got: bbb
Watcher #3 got: ccc
Watcher #4 got: ddd
Watcher #5 got: eee
but however in fact it is:
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyWatcher
CubbyFiller, item = aaa
CubbyFiller, item = bbb
CubbyFiller, item = ccc
Watcher #1 got: aaa
CubbyFiller, item = ddd
CubbyFiller, item = eee
Watcher #2 got: bbb
Watcher #3 got: ccc
Watcher #4 got: ddd
Watcher #5 got: eee
Can any one explain why??
thanks

Answer 1

I think this is the right code. For a single item queue like your CubbyHole, a user's sleep() should have no effect on the overall program execution.
/* queue: CubbyHole.java is same as before */
/* users:               */
public class TestCubbyHole {
  public static void main(String[] args) {
    Thread mainThread = Thread.currentThread();
    CubbyHole c = new CubbyHole();
    new CubbyWatcher(1, c);
    new CubbyWatcher(2, c);
    new CubbyWatcher(3, c);
    new CubbyWatcher(4, c);
    new CubbyWatcher(5, c);
    new CubbyWatcher(6, c);
    for(int ii = 0 ; ii < args.length; ii++) {
      new CubbyFiller(args[ii], c);
    try {
      System.in.read();
    } catch (java.io.IOException ioe) {
  static class CubbyWatcher implements Runnable {
    int id;
    CubbyHole theCubbyHole;
    public CubbyWatcher(int id, CubbyHole c) {
      this.id = id;
      theCubbyHole = c;
      System.out.println("CubbyWatcher");
      Thread t = new Thread(this);
      t.setDaemon(true);
      t.start();
    public void run() {
      while(true) {
        try {
synchronized(theCubbyHole){
          Object o = theCubbyHole.get();
          System.out.println("Watcher #" + id +
              " got: " + o);
        } catch (InterruptedException ie) {
  static class CubbyFiller implements Runnable {
    Object item;
    CubbyHole theCubbyHole;
    public CubbyFiller(Object i, CubbyHole c) {
      item = i;
      theCubbyHole = c;
//     System.out.println("CubbyFiller" + ", item = " + item);
      Thread t = new Thread(this);
      t.setDaemon(true);
      t.start();
    public void run() {
      Thread me = Thread.currentThread();
      int waitTime = (int)(Math.random() * 1000);
      try {
        me.sleep(waitTime);
synchronized(theCubbyHole){
        theCubbyHole.put(item);
      System.out.println("CubbyFiller put" + ", item = " + item);
      } catch (InterruptedException ie) {
}