AlphanumComparator.java

/*******************************************************************************
 * Copyright 2013 André Rouél
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/
package net.sf.uadetector.internal.util;

/*
 * The Alphanum Algorithm is an improved sorting algorithm for strings
 * containing numbers.  Instead of sorting numbers in ASCII order like
 * a standard sort, this algorithm sorts numbers in numeric order.
 *
 * The Alphanum Algorithm is discussed at http://www.DaveKoelle.com
 *
 *
 * 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 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

import java.io.Serializable;
import java.util.Comparator;

/**
 * This is an updated version with enhancements made by Daniel Migowski, Andre Bogus, and David Koelle
 * 
 * To convert to use Templates (Java 1.5+): - Change "implements Comparator" to "implements Comparator<String>" - Change
 * "compare(Object o1, Object o2)" to "compare(String s1, String s2)" - Remove the type checking and casting in
 * compare().
 * 
 * To use this class: Use the static "sort" method from the java.util.Collections class: Collections.sort(your list, new
 * AlphanumComparator());
 */
public final class AlphanumComparator implements Comparator<String>, Serializable {

    private static final long serialVersionUID = 5727692755534146935L;

    protected static int compareDigits(final String s1, final String s2) {
        int thisMarker = 0;
        int thatMarker = 0;
        final int s1Length = s1.length();
        final int s2Length = s2.length();

        while (thisMarker < s1Length && thatMarker < s2Length) {
            final String thisChunk = getChunk(s1, s1Length, thisMarker);
            thisMarker += thisChunk.length();

            final String thatChunk = getChunk(s2, s2Length, thatMarker);
            thatMarker += thatChunk.length();

            // If both chunks contain numeric characters, sort them numerically
            int result = 0;
            if (isDigit(thisChunk.charAt(0)) && isDigit(thatChunk.charAt(0))) {
                // Simple chunk comparison by length.
                final int thisChunkLength = thisChunk.length();
                result = thisChunkLength - thatChunk.length();
                // If equal, the first different number counts
                if (result == 0) {
                    for (int i = 0; i < thisChunkLength; i++) {
                        result = thisChunk.charAt(i) - thatChunk.charAt(i);
                        if (result != 0) {
                            return result;
                        }
                    }
                }
            } else {
                result = thisChunk.compareTo(thatChunk);
            }

            if (result != 0) {
                return result;
            }
        }

        return s1Length - s2Length;
    }

    /**
     * Length of string is passed in for improved efficiency (only need to calculate it once)
     */
    private static String getChunk(final String s, final int slength, int marker) {
        final StringBuilder chunk = new StringBuilder();
        char c = s.charAt(marker);
        chunk.append(c);
        marker++;
        if (isDigit(c)) {
            while (marker < slength) {
                c = s.charAt(marker);
                if (!isDigit(c)) {
                    break;
                }
                chunk.append(c);
                marker++;
            }
        } else {
            while (marker < slength) {
                c = s.charAt(marker);
                if (isDigit(c)) {
                    break;
                }
                chunk.append(c);
                marker++;
            }
        }
        return chunk.toString();
    }

    private static boolean isDigit(final char ch) {
        return ch >= 48 && ch <= 57;
    }

    @Override
    public int compare(final String a, final String b) {
        int result = 0;
        if (a == null) {
            if (b != null) {
                result = -1;
            }
        } else {
            if (b == null) {
                result = 1;
            } else {
                result = compareDigits(a, b);
            }
        }
        return result;
    }

}