/*
* ---------------------------------------------------------------------------
* Copyright (C) 2010 Felipe Meneguzzi
* JavaGP is distributed under LGPL. See file LGPL.txt in this directory.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* To contact the author:
* http://www.meneguzzi.eu/felipe/contact.html
* ---------------------------------------------------------------------------
*/
package graphplan.flyweight;
import graphplan.domain.Proposition;
import graphplan.domain.jason.PropositionImpl;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Set;
/**
* A factory class to be used in the creation and maintenance of
* propositions for our planning system using the flyweight pattern.
* XXX It may have to be modified if multiple instances of the planner are to be used
* @author Felipe Meneguzzi
*
*/
public class PropositionFactory {
private static PropositionFactory propositionFactory = null;
/**
* Returns the singleton <code>PropositionFactory</code> instance.
* @return
*/
public static final PropositionFactory getInstance() {
if(propositionFactory == null) {
propositionFactory = new PropositionFactory();
}
return propositionFactory;
}
public static final void reset() {
propositionFactory.resetPropositionFactory();
}
private Hashtable<String, Proposition> propositionInstances;
private PropositionFactory() {
this.propositionInstances = new Hashtable<String, Proposition>();
}
/**
* Returns a lightweight proposition.
* @param propositionSignature
* @return
*/
public final Proposition getProposition(String propositionSignature) {
if(!propositionInstances.containsKey(propositionSignature)) {
PropositionImpl proposition = new PropositionImpl(propositionSignature);
propositionInstances.put(propositionSignature, proposition);
return proposition;
}
return propositionInstances.get(propositionSignature);
}
/**
* Helper method for instantiating multiple propositions, mainly used for testing.
* @param propositionSignatures
* @return
*/
public Proposition []getPropositions(String []propositionSignatures) {
Proposition propositions[] = new Proposition[propositionSignatures.length];
for (int i = 0; i < propositionSignatures.length; i++) {
propositions[i] = getProposition(propositionSignatures[i]);
}
return propositions;
}
/**
* Resets the proposition factory so that it is detached from all flyweight
* propositions created so far. Invoke this method with caution.
*
*/
protected final void resetPropositionFactory() {
this.propositionInstances.clear();
}
/**
* Returns a unique signature for any list of propositions.
* @param propositions
* @return
*/
public String getGoalsSignature(Set<Proposition> propositions) {
final StringBuilder builder = new StringBuilder();
for(Proposition prop : propositions) {
builder.append(prop.hashCode());
}
return builder.toString();
}
/**
* A utility function that returns an empty proposition iterator
* @return
*/
public static Iterator<Proposition> getEmptyIterator() {
Iterator<Proposition> iterator = new Iterator<Proposition>() {
public boolean hasNext() {return false;}
public Proposition next() {return null;}
public void remove() {}
};
return iterator;
}
}