public interface IObservable
{
	void Register(Console o);
	void Unregister(Console o);
	void Notify() throws InterruptedException;
}
 
public class Timer implements IObservable
{
	private int m_interval;
	private boolean m_enabled;
	private ArrayList<Console> subscribers = new ArrayList<Console>();
 
	public Timer(int interval)
	{
		m_interval = interval;
		m_enabled = false;
	}
 
	public int getInterval()
	{
		return m_interval;
	}
 
	public void setInterval(int interval)
	{
		this.m_interval = interval;
	}
 
	public boolean isEnabled()
	{
		return m_enabled;
	}
 
	public void setEnabled(boolean enabled)
	{
		this.m_enabled = enabled;
	}
 
	@Override
	public void Notify() throws InterruptedException
	{
		if (isEnabled())
		{
			for (int i=0; i <= subscribers.size()-1; ++i)
			{
				Thread.sleep(m_interval);
				subscribers.get(i).onAction();
			}
		}
	}
 
	@Override
	public void Unregister(Console subscriber)
	{
		subscribers.remove(subscriber);
	}
 
	@Override
	public void Register(Console subscriber)
	{
		subscribers.add(subscriber);
	}
}
public class Console
{
	public void onAction()
	{
		// Bu metot periyodik olarak sistem saatini 
                //   ekrana basar
		Calendar c = Calendar.getInstance();
		System.out.println(c.getTime());
	}
}