AlphaNumComparator.java

package io.blobkeeper.common.util;

import java.util.Comparator;

/*
 * Copyright (C) 2015 by Denis M. Gabaydulin
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 *
 *
 * This is an updated version with enhancements made by Daniel Migowski,
 * Andre Bogus, and David Koelle.
 */

public class AlphaNumComparator implements Comparator<String> {
    public AlphaNumComparator() {
    }

    @Override
    public int compare(String o1, String o2) {
        if (o1 == null || o2 == null) {
            return 0;
        }

        int thisMarker = 0;
        int thatMarker = 0;
        int s1Length = o1.length();
        int s2Length = o2.length();

        while (thisMarker < s1Length && thatMarker < s2Length) {
            String thisChunk = getChunk(o1, s1Length, thisMarker);
            thisMarker += thisChunk.length();

            String thatChunk = getChunk(o2, 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.
                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;
    }

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

    /**
     * Length of string is passed in for improved efficiency (only need to calculate it once)
     */
    private String getChunk(String s, int slength, int marker) {
        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();
    }
}