MessageQueue.java

public class MessageQueue<T> {

private static final int MAX_SIZE = 255;
	
	private T[] messages;
	private int lastReadIndex;
	private int lastInsertIndex;
	
	private int adjustIndex(int index) {
		if (index >= MAX_SIZE) {
			return 0;
		}
		return index;
	}
	
	/**
	 * Constructor of the {@link MessageQueue}
	 * 
	 * @author Mischa
	 */
	@SuppressWarnings("unchecked") // Java doesn't like to create an Array of a generic type...
	public MessageQueue() {
		messages = (T[]) new Object[MAX_SIZE];
	}
	
	/**
	 * Pushes a new entry into the queue.
	 * This function will block when the queue is full.
	 * 
	 * @param msg The entry to push on the stack
	 * @throws InterruptedException
	 */
	public synchronized void push(T msg) throws InterruptedException {
		int newIndex = adjustIndex(lastInsertIndex + 1);
		
		// Check if we can push the message
		while (messages[newIndex] != null) {
			wait();
		}
		
		// Push the message
		messages[newIndex] = msg;
		lastInsertIndex = newIndex;
		notifyAll();
	}
	
	/**
	 * Pulls one entry from the queue.
	 * The entry will be returned and removed from the queue.
	 * 
	 * @return The entry from the queue
	 */
	public synchronized T pull() {
		int newIndex = adjustIndex(lastReadIndex + 1);
		
		T shouldReturn = messages[newIndex];
		messages[newIndex] = null;
		lastReadIndex = newIndex;
		notifyAll();
		return shouldReturn;
	}
	
	/**
	 * Checks if there is an entry in the queue.
	 * 
	 * @return <code>true</code>, when there is an entry in the queue
	 */
	public synchronized Boolean hasMessage() {
		if (lastInsertIndex > -1) {
			int newIndex = adjustIndex(lastReadIndex + 1);
		
			if (messages[newIndex] != null) {
				return true;
			}
		}
	
		return false;
	}
}