SoftHashMap.java Source code

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Here is the source code for SoftHashMap.java

Source

/*
 * dbXML - Native XML Database
 * Copyright (C) 1999-2004  The dbXML Group, L.L.C.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 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.
 *
 * $Id: SoftHashMap.java,v 1.2 2004/02/12 00:17:58 bradford Exp $
 */

import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * SoftHashMap
 */

public final class SoftHashMap extends AbstractMap {
    private Map hash = new HashMap();
    private final ReferenceQueue queue = new ReferenceQueue();

    public SoftHashMap() {
    }

    public Object get(Object key) {
        Object res = null;
        SoftReference sr = (SoftReference) hash.get(key);
        if (sr != null) {
            res = sr.get();
            if (res == null)
                hash.remove(key);
        }
        return res;
    }

    private void processQueue() {
        for (;;) {
            SoftValue sv = (SoftValue) queue.poll();
            if (sv != null)
                hash.remove(sv.key);
            else
                return;
        }
    }

    public Object put(Object key, Object value) {
        processQueue();
        return hash.put(key, new SoftValue(value, key, queue));
    }

    public Object remove(Object key) {
        processQueue();
        return hash.remove(key);
    }

    public void clear() {
        processQueue();
        hash.clear();
    }

    public int size() {
        processQueue();
        return hash.size();
    }

    public Set entrySet() {
        /** @todo Figure this out */
        throw new UnsupportedOperationException();
    }

    /**
     * SoftValue
     */

    private static class SoftValue extends SoftReference {
        private final Object key;

        private SoftValue(Object k, Object key, ReferenceQueue q) {
            super(k, q);
            this.key = key;
        }
    }
}