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Jadex Rules is a small lightweight rule engine, which currently employs the well-known Rete algorithm for highly efficient rule matching. Jadex rules is therefore similar to other rule engines like JESS and Drools. Despite the similarities there are also important differences between these systems: * Jadex Rules is very small and intended to be used as component of other software. Even though rules can be specified in a Java dialect as well as (a small variation of) the CLIPS language its primary usage is on the API level. Jadex Rules is currently the core component of the Jadex BDI reasoning engine. * Jadex Rules cleanly separates between state and rule representation. This allows the state implementation as well as the matcher to be flexibly exchanged. Some experiments have e.g. been conducted with a Jena representation. Regarding the matcher, it is planned to support also the Treat algorithm, which has a lower memory footprint than Rete. * Jadex Rules pays close attention to rule debugging. The state as well as the rete engine can be observed at runtime. The rule debugger provides functionalities to execute a rule program stepwise and also use rule breakpoints to stop the execution at those points.

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package jadex.rules.rulesystem;

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 *  LIFO agenda.
 */
public class LIFOAgenda extends AbstractAgenda
{
	//-------- attributes --------
	
	/** The activations. */
	protected Set activations;
	
	/** The next activation (selected by strategy or manually form outside for debugging). */
	protected Activation next;
	
	//-------- constructors --------
	
	/**
	 *  Create a new agenda.
	 */
	public LIFOAgenda()
	{
		this.activations = new LinkedHashSet();
	}
	
	/**
	 *  Add a new activation.
	 *  @param act The activation.
	 */
	public void addActivation(Activation act)
	{
		next = act;
		this.activations.add(act);
		state++;
		notifyListeners();
	}
	
	/**
	 *  Remove an activation
	 *  @param act The activation.
	 */
	public void removeActivation(Activation act)
	{
		this.activations.remove(act);
		if(act.equals(next))
			next = null;
		state++;
		notifyListeners();
	}
	
	/**
	 *  Get the current activations.
	 *  @return The activations.
	 */
	public Collection getActivations()
	{
		return activations;
	}
	
	/**
	 *  Test if the agenda is empty.
	 *  @return True if is empty.
	 */
	public boolean isEmpty()
	{
		return activations.isEmpty();
	}
	
	/**
	 *  Get the next activation.
	 *  @return The next activation.
	 */ 
	public Activation getNextActivation()
	{
		Activation ret	= next;
		if(ret==null && activations.size()>0)
		{
			Object	oret	= null;
			for(Iterator it=activations.iterator(); it.hasNext(); )
				oret = it.next();
			ret	= (Activation)oret;
		}
		return ret;
	}

	/**
	 *  Set the next activation.
	 */ 
	public void setNextActivation(Activation next)
	{
		if(activations.contains(next))
		{
			this.next	= next;
		}
		else
		{
			throw new RuntimeException("Activation not in agenda: "+next+", "+this);
		}
		notifyListeners();
	}
}