org.oss.pdfreporter.crosstabs.fill.calculation.ArbitraryRankComparator.java Source code

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/*
 * JasperReports - Free Java Reporting Library.
 * Copyright (C) 2001 - 2011 Jaspersoft Corporation. All rights reserved.
 * http://www.jaspersoft.com
 *
 * Unless you have purchased a commercial license agreement from Jaspersoft,
 * the following license terms apply:
 *
 * This program is part of JasperReports.
 *
 * JasperReports 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 3 of the License, or
 * (at your option) any later version.
 *
 * JasperReports 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 JasperReports. If not, see <http://www.gnu.org/licenses/>.
 */
package org.oss.pdfreporter.crosstabs.fill.calculation;

import java.util.Comparator;

import org.oss.pdfreporter.engine.JRRuntimeException;
import org.oss.pdfreporter.uses.org.apache.commons.collections.ReferenceMap;

/**
 * A comparator that assigns arbitrary ranks to objects and uses the ranks
 * to impose an arbitrary order on them.
 * 
 * @author Lucian Chirita (lucianc@users.sourceforge.net)
 * @version $Id: ArbitraryRankComparator.java 4595 2011-09-08 15:55:10Z teodord $
 */
public class ArbitraryRankComparator implements Comparator<Object> {

    // using a weak ref map to store ranks per objects
    private final ReferenceMap ranks = new ReferenceMap(ReferenceMap.WEAK, ReferenceMap.HARD);
    private long rankCounter = Long.MIN_VALUE;

    public int compare(Object o1, Object o2) {
        if (o1 == o2 || o1.equals(o2)) {
            return 0;
        }

        long rank1 = rank(o1);
        long rank2 = rank(o2);

        if (rank1 < rank2) {
            return -1;
        }

        if (rank1 > rank2) {
            return 1;
        }

        // this should not happen
        throw new JRRuntimeException("Arbitrary rank comparator found two objects with the same rank");
    }

    protected synchronized long rank(Object o) {
        long rank;
        Long existingRank = (Long) ranks.get(o);
        if (existingRank == null) {
            rank = rankCounter;

            ++rankCounter;
            // check for overflow, very unlikely
            if (rankCounter == Long.MIN_VALUE) {
                throw new JRRuntimeException("Arbitrary rank comparator has overflowed");
            }

            ranks.put(o, new Long(rank));
        } else {
            rank = existingRank.longValue();
        }
        return rank;
    }

}