001    /*
002      Copyright (C) 2001 Laurent Martelli
003    
004      This program is free software; you can redistribute it and/or modify
005      it under the terms of the GNU Lesser General Public License as
006      published by the Free Software Foundation; either version 2 of the
007      License, or (at your option) any later version.
008    
009      This program is distributed in the hope that it will be useful,
010      but WITHOUT ANY WARRANTY; without even the implied warranty of
011      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
012      GNU Lesser General Public License for more details.
013    
014      You should have received a copy of the GNU Lesser General Public License
015      along with this program; if not, write to the Free Software
016      Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
017    
018    package org.objectweb.jac.util;
019    
020    import java.util.HashMap;
021    
022    
023    /**
024     * Implements a map whose data may be shared between several
025     * instances. It has the benefit of having a fast clone() method which
026     * only duplicates the data when needed.
027     */
028    public class SharedMap implements Cloneable {
029       HashMap map;
030       boolean shared=false;
031       public SharedMap() {
032          map = new HashMap();
033       }
034       public SharedMap(HashMap map) {
035          this.map = map;
036       }
037       SharedMap(HashMap map, boolean shared) {
038          this.map = map;
039          this.shared = shared;
040       }
041       public Object clone() {
042          shared = true;
043          return new SharedMap(map,true);
044       }
045       public Object get(Object key) {
046          return map.get(key);
047       }
048       public synchronized void put(Object key, Object value) {
049          if (shared) {
050             //System.out.println("cloning shared map");
051             map = (HashMap)map.clone();
052             shared = false;
053          }
054          map.put(key,value);
055       }
056    }