/* File: MultiHashtable.java
 * Contains: A table associating each key with more than one value
 * Author: Jeff Dalton <J.Dalton@ed.ac.uk>
 * Created: August 1998
 * Updated: Sun Aug 23 23:04:22 1998 by Jeff Dalton
 * Copyright: (c) 1998, AIAI, University of Edinburgh
 */

package ix.util;

import java.util.Hashtable;
import java.util.Vector;

/**
 * A MultiHashtable is (by weak analogy with "multiset") a Hashtable
 * that maps each key to a collection of values.  <i>For now, the collection
 * will always be a Vector, and there'll be no check for duplicate values.
 * Eventually, this should be generalized.</i>
 */

public class MultiHashtable extends Hashtable {

    public MultiHashtable() {
	super();
    }

    public synchronized Object put(Object key, Object value) {
	Vector already = (Vector)get(key);
	if (already == null) {
	    already = new Vector();
	    super.put(key, already);
	}
	already.addElement(value);
	return already;
    }

}