Metaphone.java
/*
* 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.
*/
package org.apache.commons.codec.language;
import org.apache.commons.codec.EncoderException;
import org.apache.commons.codec.StringEncoder;
/**
* Encodes a string into a Metaphone value.
* <p>
* Initial Java implementation by <CITE>William B. Brogden. December, 1997</CITE>.
* Permission given by <CITE>wbrogden</CITE> for code to be used anywhere.
* </p>
* <p>
* <CITE>Hanging on the Metaphone</CITE> by <CITE>Lawrence Philips</CITE> in <CITE>Computer Language of Dec. 1990,
* p 39.</CITE>
* </p>
* <p>
* Note, that this does not match the algorithm that ships with PHP, or the algorithm found in the Perl implementations:
* </p>
* <ul>
* <li><a href="https://search.cpan.org/~mschwern/Text-Metaphone-1.96/Metaphone.pm">Text:Metaphone-1.96</a>
* (broken link 4/30/2013) </li>
* <li><a href="https://metacpan.org/source/MSCHWERN/Text-Metaphone-1.96//Metaphone.pm">Text:Metaphone-1.96</a>
* (link checked 4/30/2013) </li>
* </ul>
* <p>
* They have had undocumented changes from the originally published algorithm.
* For more information, see <a href="https://issues.apache.org/jira/browse/CODEC-57">CODEC-57</a>.
* </p>
* <p>
* This class is conditionally thread-safe.
* The instance field for maximum code length is mutable {@link #setMaxCodeLen(int)}
* but is not volatile, and accesses are not synchronized.
* If an instance of the class is shared between threads, the caller needs to ensure that suitable synchronization
* is used to ensure safe publication of the value between threads, and must not invoke {@link #setMaxCodeLen(int)}
* after initial setup.
* </p>
*/
public class Metaphone implements StringEncoder {
/**
* Five values in the English language
*/
private static final String VOWELS = "AEIOU";
/**
* Variable used in Metaphone algorithm
*/
private static final String FRONTV = "EIY";
/**
* Variable used in Metaphone algorithm
*/
private static final String VARSON = "CSPTG";
/**
* The max code length for metaphone is 4
*/
private int maxCodeLen = 4;
/**
* Encodes an Object using the metaphone algorithm. This method
* is provided in order to satisfy the requirements of the
* Encoder interface, and will throw an EncoderException if the
* supplied object is not of type {@link String}.
*
* @param obj Object to encode
* @return An object (or type {@link String}) containing the
* metaphone code which corresponds to the String supplied.
* @throws EncoderException if the parameter supplied is not
* of type {@link String}
*/
@Override
public Object encode(final Object obj) throws EncoderException {
if (!(obj instanceof String)) {
throw new EncoderException("Parameter supplied to Metaphone encode is not of type java.lang.String");
}
return metaphone((String) obj);
}
/**
* Encodes a String using the Metaphone algorithm.
*
* @param str String object to encode
* @return The metaphone code corresponding to the String supplied
*/
@Override
public String encode(final String str) {
return metaphone(str);
}
/**
* Returns the maxCodeLen.
* @return int
*/
public int getMaxCodeLen() { return this.maxCodeLen; }
private boolean isLastChar(final int wdsz, final int n) {
return n + 1 == wdsz;
}
/**
* Tests is the metaphones of two strings are identical.
*
* @param str1 First of two strings to compare
* @param str2 Second of two strings to compare
* @return {@code true} if the metaphones of these strings are identical,
* {@code false} otherwise.
*/
public boolean isMetaphoneEqual(final String str1, final String str2) {
return metaphone(str1).equals(metaphone(str2));
}
private boolean isNextChar(final StringBuilder string, final int index, final char c) {
boolean matches = false;
if (index >= 0 && index < string.length() - 1) {
matches = string.charAt(index + 1) == c;
}
return matches;
}
private boolean isPreviousChar(final StringBuilder string, final int index, final char c) {
boolean matches = false;
if (index > 0 && index < string.length()) {
matches = string.charAt(index - 1) == c;
}
return matches;
}
private boolean isVowel(final StringBuilder string, final int index) {
return VOWELS.indexOf(string.charAt(index)) >= 0;
}
/**
* Find the metaphone value of a String. This is similar to the
* soundex algorithm, but better at finding similar sounding words.
* All input is converted to upper case.
* Limitations: Input format is expected to be a single ASCII word
* with only characters in the A - Z range, no punctuation or numbers.
*
* @param txt String to find the metaphone code for
* @return A metaphone code corresponding to the String supplied
*/
public String metaphone(final String txt) {
boolean hard = false;
final int txtLength;
if (txt == null || (txtLength = txt.length()) == 0) {
return "";
}
// single character is itself
if (txtLength == 1) {
return txt.toUpperCase(java.util.Locale.ENGLISH);
}
final char[] inwd = txt.toUpperCase(java.util.Locale.ENGLISH).toCharArray();
final StringBuilder local = new StringBuilder(40); // manipulate
final StringBuilder code = new StringBuilder(10); // output
// handle initial 2 characters exceptions
switch (inwd[0]) {
case 'K':
case 'G':
case 'P': /* looking for KN, etc */
if (inwd[1] == 'N') {
local.append(inwd, 1, inwd.length - 1);
} else {
local.append(inwd);
}
break;
case 'A': /* looking for AE */
if (inwd[1] == 'E') {
local.append(inwd, 1, inwd.length - 1);
} else {
local.append(inwd);
}
break;
case 'W': /* looking for WR or WH */
if (inwd[1] == 'R') { // WR -> R
local.append(inwd, 1, inwd.length - 1);
break;
}
if (inwd[1] == 'H') {
local.append(inwd, 1, inwd.length - 1);
local.setCharAt(0, 'W'); // WH -> W
} else {
local.append(inwd);
}
break;
case 'X': /* initial X becomes S */
inwd[0] = 'S';
local.append(inwd);
break;
default:
local.append(inwd);
} // now local has working string with initials fixed
final int wdsz = local.length();
int n = 0;
while (code.length() < this.getMaxCodeLen() && n < wdsz) { // max code size of 4 works well
final char symb = local.charAt(n);
// remove duplicate letters except C
if (symb != 'C' && isPreviousChar(local, n, symb)) {
n++;
} else { // not dup
switch (symb) {
case 'A':
case 'E':
case 'I':
case 'O':
case 'U':
if (n == 0) {
code.append(symb);
}
break; // only use vowel if leading char
case 'B':
if (isPreviousChar(local, n, 'M') && isLastChar(wdsz, n)) { // B is silent if word ends in MB
break;
}
code.append(symb);
break;
case 'C': // lots of C special cases
/* discard if SCI, SCE or SCY */
if (isPreviousChar(local, n, 'S') && !isLastChar(wdsz, n) && FRONTV.indexOf(local.charAt(n + 1)) >= 0) {
break;
}
if (regionMatch(local, n, "CIA")) { // "CIA" -> X
code.append('X');
break;
}
if (!isLastChar(wdsz, n) && FRONTV.indexOf(local.charAt(n + 1)) >= 0) {
code.append('S');
break; // CI,CE,CY -> S
}
if (isPreviousChar(local, n, 'S') && isNextChar(local, n, 'H')) { // SCH->sk
code.append('K');
break;
}
if (isNextChar(local, n, 'H')) { // detect CH
if (n == 0 && wdsz >= 3 && isVowel(local, 2)) { // CH consonant -> K consonant
code.append('K');
} else {
code.append('X'); // CHvowel -> X
}
} else {
code.append('K');
}
break;
case 'D':
if (!isLastChar(wdsz, n + 1) && isNextChar(local, n, 'G') && FRONTV.indexOf(local.charAt(n + 2)) >= 0) { // DGE DGI DGY -> J
code.append('J');
n += 2;
} else {
code.append('T');
}
break;
case 'G': // GH silent at end or before consonant
if (isLastChar(wdsz, n + 1) && isNextChar(local, n, 'H')) {
break;
}
if (!isLastChar(wdsz, n + 1) && isNextChar(local, n, 'H') && !isVowel(local, n + 2)) {
break;
}
if (n > 0 && (regionMatch(local, n, "GN") || regionMatch(local, n, "GNED"))) {
break; // silent G
}
// NOTE: Given that duplicated chars are removed, I don't see how this can ever be true
hard = isPreviousChar(local, n, 'G');
if (!isLastChar(wdsz, n) && FRONTV.indexOf(local.charAt(n + 1)) >= 0 && !hard) {
code.append('J');
} else {
code.append('K');
}
break;
case 'H':
if (isLastChar(wdsz, n)) {
break; // terminal H
}
if (n > 0 && VARSON.indexOf(local.charAt(n - 1)) >= 0) {
break;
}
if (isVowel(local, n + 1)) {
code.append('H'); // Hvowel
}
break;
case 'F':
case 'J':
case 'L':
case 'M':
case 'N':
case 'R':
code.append(symb);
break;
case 'K':
if (n > 0) { // not initial
if (!isPreviousChar(local, n, 'C')) {
code.append(symb);
}
} else {
code.append(symb); // initial K
}
break;
case 'P':
if (isNextChar(local, n, 'H')) {
// PH -> F
code.append('F');
} else {
code.append(symb);
}
break;
case 'Q':
code.append('K');
break;
case 'S':
if (regionMatch(local, n, "SH") || regionMatch(local, n, "SIO") || regionMatch(local, n, "SIA")) {
code.append('X');
} else {
code.append('S');
}
break;
case 'T':
if (regionMatch(local, n, "TIA") || regionMatch(local, n, "TIO")) {
code.append('X');
break;
}
if (regionMatch(local, n, "TCH")) {
// Silent if in "TCH"
break;
}
// substitute numeral 0 for TH (resembles theta after all)
if (regionMatch(local, n, "TH")) {
code.append('0');
} else {
code.append('T');
}
break;
case 'V':
code.append('F');
break;
case 'W':
case 'Y': // silent if not followed by vowel
if (!isLastChar(wdsz, n) && isVowel(local, n + 1)) {
code.append(symb);
}
break;
case 'X':
code.append('K');
code.append('S');
break;
case 'Z':
code.append('S');
break;
default:
// do nothing
break;
} // end switch
n++;
} // end else from symb != 'C'
if (code.length() > this.getMaxCodeLen()) {
code.setLength(this.getMaxCodeLen());
}
}
return code.toString();
}
private boolean regionMatch(final StringBuilder string, final int index, final String test) {
boolean matches = false;
if (index >= 0 && index + test.length() - 1 < string.length()) {
final String substring = string.substring(index, index + test.length());
matches = substring.equals(test);
}
return matches;
}
/**
* Sets the maxCodeLen.
* @param maxCodeLen The maxCodeLen to set
*/
public void setMaxCodeLen(final int maxCodeLen) { this.maxCodeLen = maxCodeLen; }
}