AlphanumComparator.java

package games.strategy.util;

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.tools.Collections class:
 * Collections.sort(your list, new AlphanumComparator());
 */
public class AlphanumComparator implements Comparator<String> {
  private boolean isDigit(final 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(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();
  }

  @Override
  public int compare(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;
  }
}