basiceventstream.java

最大熵模型源代码

///////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2001 Jason Baldridge
//
// 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 General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//////////////////////////////////////////////////////////////////////////////   
package opennlp.maxent;

/**
 * A object which can deliver a stream of training events assuming
 * that each event is represented as a space separated list containing
 * all the contextual predicates, with the last item being the
 * outcome, e.g.: 
 *
 * <p> cp_1 cp_2 ... cp_n outcome
 *
 * @author      Jason Baldridge
 * @version $Revision: 1.1 $, $Date: 2001/11/20 17:05:37 $ 
*/
public class BasicEventStream implements EventStream {
    ContextGenerator _cg = new BasicContextGenerator();
    DataStream _ds;
    Event _next;

    public BasicEventStream (DataStream ds) {
	_ds = ds;
	if (_ds.hasNext())
	    _next = createEvent((String)_ds.nextToken());
    }

    /**
     * Returns the next Event object held in this EventStream.  Each call to nextEvent advances the EventStream.
     *
     * @return the Event object which is next in this EventStream
     */
    public Event nextEvent () {
	while (_next == null && _ds.hasNext())
	    _next = createEvent((String)_ds.nextToken());

	Event current = _next;
	if (_ds.hasNext()) {
	    _next = createEvent((String)_ds.nextToken());
	}
	else {
	    _next = null;
	}
	return current;
    }
 
    /**
     * Test whether there are any Events remaining in this EventStream.
     *
     * @return true if this EventStream has more Events
     */
    public boolean hasNext () {
	while (_next == null && _ds.hasNext())
	    _next = createEvent((String)_ds.nextToken());
	return _next != null;
    }

    private Event createEvent(String obs) {
	int lastSpace = obs.lastIndexOf(' ');
	if (lastSpace == -1) 
	    return null;
	else
	    return new Event(obs.substring(lastSpace+1),
			     _cg.getContext(obs.substring(0, lastSpace)));
    }


}