Soundex.java Source code

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Here is the source code for Soundex.java

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/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.com/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun's Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun's, and James Gosling's,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
/**
 * Soundex - the Soundex Algorithm, as described by Knuth
 * <p>
 * This class implements the soundex algorithm as described by Donald
 * Knuth in Volume 3 of <I>The Art of Computer Programming</I>.  The
 * algorithm is intended to hash words (in particular surnames) into
 * a small space using a simple model which approximates the sound of
 * the word when spoken by an English speaker.  Each word is reduced
 * to a four character string, the first character being an upper case
 * letter and the remaining three being digits. Double letters are
 * collapsed to a single digit.
 * 
 * <h2>EXAMPLES</h2>
 * Knuth's examples of various names and the soundex codes they map
 * to are:
 * <b>Euler, Ellery -> E460
 * <b>Gauss, Ghosh -> G200
 * <b>Hilbert, Heilbronn -> H416
 * <b>Knuth, Kant -> K530
 * <b>Lloyd, Ladd -> L300
 * <b>Lukasiewicz, Lissajous -> L222
 * 
 * <h2>LIMITATIONS</h2>
 * As the soundex algorithm was originally used a <B>long</B> time ago
 * in the United States of America, it uses only the English alphabet
 * and pronunciation.
 * <p>
 * As it is mapping a large space (arbitrary length strings) onto a
 * small space (single letter plus 3 digits) no inference can be made
 * about the similarity of two strings which end up with the same
 * soundex code.  For example, both "Hilbert" and "Heilbronn" end up
 * with a soundex code of "H416".
 * <p>
 * The soundex() method is static, as it maintains no per-instance
 * state; this means you never need to instantiate this class.
 *
 * @author Perl implementation by Mike Stok (<stok@cybercom.net>) from
 * the description given by Knuth.  Ian Phillips (<ian@pipex.net>) and
 * Rich Pinder (<rpinder@hsc.usc.edu>) supplied ideas and spotted
 * mistakes.
 * @author Ian Darwin, http://www.darwinsys.com/ (Java Version)
 * @version $Id: Soundex.java,v 1.9 2004/02/23 00:30:49 ian Exp $
 */
public class Soundex {

    /* Implements the mapping
     * from: AEHIOUWYBFPVCGJKQSXZDTLMNR
     * to:   00000000111122222222334556
     */
    public static final char[] MAP = {
            //A  B   C   D   E   F   G   H   I   J   K   L   M
            '0', '1', '2', '3', '0', '1', '2', '0', '0', '2', '2', '4', '5',
            //N  O   P   W   R   S   T   U   V   W   X   Y   Z
            '5', '0', '1', '2', '6', '2', '3', '0', '1', '0', '2', '0', '2' };

    /** Convert the given String to its Soundex code.
     * @return null If the given string can't be mapped to Soundex.
     */
    public static String soundex(String s) {

        // Algorithm works on uppercase (mainframe era).
        String t = s.toUpperCase();

        StringBuffer res = new StringBuffer();
        char c, prev = '?';

        // Main loop: find up to 4 chars that map.
        for (int i = 0; i < t.length() && res.length() < 4 && (c = t.charAt(i)) != ','; i++) {

            // Check to see if the given character is alphabetic.
            // Text is already converted to uppercase. Algorithm
            // only handles ASCII letters, do NOT use Character.isLetter()!
            // Also, skip double letters.
            if (c >= 'A' && c <= 'Z' && c != prev) {
                prev = c;

                // First char is installed unchanged, for sorting.
                if (i == 0)
                    res.append(c);
                else {
                    char m = MAP[c - 'A'];
                    if (m != '0')
                        res.append(m);
                }
            }
        }
        if (res.length() == 0)
            return null;
        for (int i = res.length(); i < 4; i++)
            res.append('0');
        return res.toString();
    }

    /** main */
    public static void main(String[] args) {
        String[] names = { "Darwin, Ian", "Davidson, Greg", "Darwent, William", "Derwin, Daemon" };
        for (int i = 0; i < names.length; i++)
            System.out.println(Soundex.soundex(names[i]) + ' ' + names[i]);
    }

}