package sharing;

import java.applet.Applet;
import java.util.ArrayList;
import java.util.List;

/**
 * A utility class of which at most one instance can exist per VM. 
 * Use Singleton.instance() to access this instance.
 * 
 * Based on http://wiki.java.net/bin/view/Javapedia/Singleton
 */
public class Singleton {
	/**
	 * The constructor is be made private to prevent others from
	 * instantiating this class.
	 */
	private Singleton() {}

	/**
	 * A handle to the unique Singleton instance.
	 */
	static private Singleton _instance = null;
	
	/**
	 * The list of "client" Applets.
	 */
	private List<Applet> clients = new ArrayList<Applet>();

	/**
	 * @return The unique instance of this class.
	 */
	static public Singleton instance() {
		if (null == _instance) {
			_instance = new Singleton();
		}
		return _instance;
	}
	
	/**
	 * Register the specified Applet as a client.
	 */
	public void register(Applet client) {
		clients.add(client);
	}
	
	/**
	 * @return The list of registered clients.
	 */
	public List<Applet> getClients() {
		return clients;
	}
}