SE450: Horstmann Chapter 9: Why is Output Corrupted?

Sometimes program gets stuck and doesn't complete
Can see problem better when turning debugging on
queue.setDebug(true);

file:horstmann/ch09_queue1/ThreadTester.java [source] [doc-public] [doc-private]

package horstmann.ch09_queue1;
/**
   This program runs two threads in parallel.
 */
public class ThreadTester
{
  public static void main(String[] args)
  {
    BoundedQueue<String> queue = new BoundedQueue<String>(10);
    queue.setDebug(true);
    final int GREETING_COUNT = 100;
    Runnable run1 = new Producer("Hello, World!",
        queue, GREETING_COUNT);
    Runnable run2 = new Producer("Goodbye, World!",
        queue, GREETING_COUNT);
    Runnable run3 = new Consumer(queue, 2 * GREETING_COUNT);

    Thread thread1 = new Thread(run1);
    Thread thread2 = new Thread(run2);
    Thread thread3 = new Thread(run3);

    thread1.start();
    thread2.start();
    thread3.start();
  }
}

file:horstmann/ch09_queue1/Producer.java [source] [doc-public] [doc-private]

package horstmann.ch09_queue1;
/**
   An action that repeatedly inserts a greeting into a queue.
 */
public class Producer implements Runnable
{
  /**
      Constructs the producer object.
      @param aGreeting the greating to insert into a queue
      @param aQueue the queue into which to insert greetings
      @param count the number of greetings to produce
   */
  public Producer(String aGreeting, BoundedQueue<String> aQueue, int count)
  {
    greeting = aGreeting;
    queue = aQueue;
    greetingCount = count;
  }

  public void run()
  {
    try
    {
      int i = 1;
      while (i <= greetingCount)
      {
        if (!queue.isFull())
        {
          queue.add(i + ": " + greeting);
          i++;
        }
        Thread.sleep((int) (Math.random() * DELAY));
      }
    }
    catch (InterruptedException exception)
    {
    }
  }

  private String greeting;
  private BoundedQueue<String> queue;
  private int greetingCount;

  private static final int DELAY = 10;
}

file:horstmann/ch09_queue1/Consumer.java [source] [doc-public] [doc-private]

package horstmann.ch09_queue1;
/**
   An action that repeatedly removes a greeting from a queue.
 */
public class Consumer implements Runnable
{
  /**
      Constructs the consumer object.
      @param aQueue the queue from which to retrieve greetings
      @param count the number of greetings to consume
   */
  public Consumer(BoundedQueue<String> aQueue, int count)
  {
    queue = aQueue;
    greetingCount = count;
  }

  public void run()
  {
    try
    {
      int i = 1;
      while (i <= greetingCount)
      {
        if (!queue.isEmpty())
        {
          String greeting = queue.remove();
          System.out.println(greeting);
          i++;
        }
        Thread.sleep((int)(Math.random() * DELAY));
      }
    }
    catch (InterruptedException exception)
    {
    }
  }

  private BoundedQueue<String> queue;
  private int greetingCount;

  private static final int DELAY = 10;
}

file:horstmann/ch09_queue1/BoundedQueue.java [source] [doc-public] [doc-private]

package horstmann.ch09_queue1;
import java.util.ArrayList;
/**
    A first-in, first-out bounded collection of objects.
 */
public class BoundedQueue<E>
{
  /**
       Constructs an empty queue.
       @param capacity the maximum capacity of the queue
   */
  public BoundedQueue(int capacity)
  {
    elements = new ArrayList<E>(capacity);
    head = 0;
    tail = 0;
    size = 0;
  }

  /**
       Removes the object at the head.
       @return the object that has been removed from the queue
       <p><b>Precondition:</b> !isEmpty()</p>
   */
  public E remove()
  {
    if (debug) System.out.print("removeFirst");
    E r = elements.get(head);
    if (debug) System.out.print(".");
    head++;
    if (debug) System.out.print(".");
    size--;
    if (head == elements.size())
    {
      if (debug) System.out.print(".");
      head = 0;
    }
    if (debug)
      System.out.println("head=" + head + ",tail=" + tail
          + ",size=" + size);
    return r;
  }

  /**
       Appends an object at the tail.
       @param newValue the object to be appended
       <p><b>Precondition:</b> !isFull();</p>
   */
  public void add(E newValue)
  {
    if (debug) System.out.print("add");
    elements.set(tail,newValue);
    if (debug) System.out.print(".");
    tail++;
    if (debug) System.out.print(".");
    size++;
    if (tail == elements.size())
    {
      if (debug) System.out.print(".");
      tail = 0;
    }
    if (debug)
      System.out.println("head=" + head + ",tail=" + tail
          + ",size=" + size);
  }

  public boolean isFull()
  {
    return size == elements.size();
  }

  public boolean isEmpty()
  {
    return size == 0;
  }

  public void setDebug(boolean newValue)
  {
    debug = newValue;
  }

  private ArrayList<E> elements;
  private int head;
  private int tail;
  private int size;
  private boolean debug;
}