Source code

001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.codec.language;
019
020import java.util.Locale;
021
022import org.apache.commons.codec.EncoderException;
023import org.apache.commons.codec.StringEncoder;
024
025/**
026 * Encodes a string into a Metaphone value.
027 * <p>
028 * Initial Java implementation by <CITE>William B. Brogden. December, 1997</CITE>.
029 * Permission given by <CITE>wbrogden</CITE> for code to be used anywhere.
030 * </p>
031 * <p>
032 * <CITE>Hanging on the Metaphone</CITE> by <CITE>Lawrence Philips</CITE> in <CITE>Computer Language of Dec. 1990,
033 * p 39.</CITE>
034 * </p>
035 * <p>
036 * Note, that this does not match the algorithm that ships with PHP, or the algorithm found in the Perl implementations:
037 * </p>
038 * <ul>
039 * <li><a href="https://search.cpan.org/~mschwern/Text-Metaphone-1.96/Metaphone.pm">Text:Metaphone-1.96</a>
040 *  (broken link 4/30/2013) </li>
041 * <li><a href="https://metacpan.org/source/MSCHWERN/Text-Metaphone-1.96//Metaphone.pm">Text:Metaphone-1.96</a>
042 *  (link checked 4/30/2013) </li>
043 * </ul>
044 * <p>
045 * They have had undocumented changes from the originally published algorithm.
046 * For more information, see <a href="https://issues.apache.org/jira/browse/CODEC-57">CODEC-57</a>.
047 * </p>
048 * <p>
049 * This class is conditionally thread-safe.
050 * The instance field for maximum code length is mutable {@link #setMaxCodeLen(int)}
051 * but is not volatile, and accesses are not synchronized.
052 * If an instance of the class is shared between threads, the caller needs to ensure that suitable synchronization
053 * is used to ensure safe publication of the value between threads, and must not invoke {@link #setMaxCodeLen(int)}
054 * after initial setup.
055 * </p>
056 */
057public class Metaphone implements StringEncoder {
058
059    /**
060     * Five values in the English language.
061     */
062    private static final String VOWELS = "AEIOU";
063
064    /**
065     * Variable used in Metaphone algorithm.
066     */
067    private static final String FRONTV = "EIY";
068
069    /**
070     * Variable used in Metaphone algorithm.
071     */
072    private static final String VARSON = "CSPTG";
073
074    /**
075     * The max code length for Metaphone is 4.
076     */
077    private int maxCodeLen = 4;
078
079    /**
080     * Constructs a new instance.
081     */
082    public Metaphone() {
083        // empty
084    }
085
086    /**
087     * 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
088     * EncoderException if the supplied object is not of type {@link String}.
089     *
090     * @param obj Object to encode.
091     * @return An object (or type {@link String}) containing the Metaphone code which corresponds to the String supplied.
092     * @throws EncoderException if the parameter supplied is not of type {@link String}.
093     */
094    @Override
095    public Object encode(final Object obj) throws EncoderException {
096        if (!(obj instanceof String)) {
097            throw new EncoderException("Parameter supplied to Metaphone encode is not of type java.lang.String");
098        }
099        return metaphone((String) obj);
100    }
101
102    /**
103     * Encodes a String using the Metaphone algorithm.
104     *
105     * @param str String object to encode.
106     * @return The Metaphone code corresponding to the String supplied.
107     */
108    @Override
109    public String encode(final String str) {
110        return metaphone(str);
111    }
112
113    /**
114     * Gets the maxCodeLen.
115     *
116     * @return the maxCodeLen.
117     */
118    public int getMaxCodeLen() {
119        return this.maxCodeLen;
120    }
121
122    private boolean isLastChar(final int wdsz, final int n) {
123        return n + 1 == wdsz;
124    }
125
126    /**
127     * Tests is the Metaphones of two strings are identical.
128     *
129     * @param str1 First of two strings to compare.
130     * @param str2 Second of two strings to compare.
131     * @return {@code true} if the Metaphones of these strings are identical, {@code false} otherwise.
132     */
133    public boolean isMetaphoneEqual(final String str1, final String str2) {
134        return metaphone(str1).equals(metaphone(str2));
135    }
136
137    private boolean isNextChar(final StringBuilder string, final int index, final char c) {
138        boolean matches = false;
139        if (index >= 0 && index < string.length() - 1) {
140            matches = string.charAt(index + 1) == c;
141        }
142        return matches;
143    }
144
145    private boolean isPreviousChar(final StringBuilder string, final int index, final char c) {
146        boolean matches = false;
147        if (index > 0 && index < string.length()) {
148            matches = string.charAt(index - 1) == c;
149        }
150        return matches;
151    }
152
153    private boolean isVowel(final StringBuilder string, final int index) {
154        return VOWELS.indexOf(string.charAt(index)) >= 0;
155    }
156
157    /**
158     * Find the Metaphone value of a String. This is similar to the
159     * Soundex algorithm, but better at finding similar sounding words.
160     * All input is converted to upper case.
161     * Limitations: Input format is expected to be a single ASCII word
162     * with only characters in the A - Z range, no punctuation or numbers.
163     *
164     * @param txt String to find the Metaphone code for.
165     * @return A Metaphone code corresponding to the String supplied.
166     */
167    public String metaphone(final String txt) {
168        boolean hard = false;
169        final int txtLength;
170        if (txt == null || (txtLength = txt.length()) == 0) {
171            return "";
172        }
173        // single character is itself
174        if (txtLength == 1) {
175            return txt.toUpperCase(Locale.ENGLISH);
176        }
177
178        final char[] inwd = txt.toUpperCase(Locale.ENGLISH).toCharArray();
179
180        final StringBuilder local = new StringBuilder(40); // manipulate
181        final StringBuilder code = new StringBuilder(10); // output
182        // handle initial 2 characters exceptions
183        switch (inwd[0]) {
184        case 'K':
185        case 'G':
186        case 'P': /* looking for KN, etc */
187            if (inwd[1] == 'N') {
188                local.append(inwd, 1, inwd.length - 1);
189            } else {
190                local.append(inwd);
191            }
192            break;
193        case 'A': /* looking for AE */
194            if (inwd[1] == 'E') {
195                local.append(inwd, 1, inwd.length - 1);
196            } else {
197                local.append(inwd);
198            }
199            break;
200        case 'W': /* looking for WR or WH */
201            if (inwd[1] == 'R') { // WR -> R
202                local.append(inwd, 1, inwd.length - 1);
203                break;
204            }
205            if (inwd[1] == 'H') {
206                local.append(inwd, 1, inwd.length - 1);
207                local.setCharAt(0, 'W'); // WH -> W
208            } else {
209                local.append(inwd);
210            }
211            break;
212        case 'X': /* initial X becomes S */
213            inwd[0] = 'S';
214            local.append(inwd);
215            break;
216        default:
217            local.append(inwd);
218        } // now local has working string with initials fixed
219
220        final int wdsz = local.length();
221        int n = 0;
222
223        while (code.length() < getMaxCodeLen() && n < wdsz) { // max code size of 4 works well
224            final char symb = local.charAt(n);
225            // remove duplicate letters except C
226            if (symb == 'C' || !isPreviousChar(local, n, symb)) {
227                // not dup
228                switch (symb) {
229                case 'A':
230                case 'E':
231                case 'I':
232                case 'O':
233                case 'U':
234                    if (n == 0) {
235                        code.append(symb);
236                    }
237                    break; // only use vowel if leading char
238                case 'B':
239                    if (isPreviousChar(local, n, 'M') && isLastChar(wdsz, n)) { // B is silent if word ends in MB
240                        break;
241                    }
242                    code.append(symb);
243                    break;
244                case 'C': // lots of C special cases
245                    /* discard if SCI, SCE or SCY */
246                    if (isPreviousChar(local, n, 'S') && !isLastChar(wdsz, n) && FRONTV.indexOf(local.charAt(n + 1)) >= 0) {
247                        break;
248                    }
249                    if (isPreviousChar(local, n, 'S') && isNextChar(local, n, 'H')) { // SCH->sk
250                        code.append('K');
251                        break;
252                    }
253                    if (regionMatch(local, n, "CIA") || isNextChar(local, n, 'H')) { // "CIA" -> X or CH -> X
254                        code.append('X');
255                        break;
256                    }
257                    if (!isLastChar(wdsz, n) && FRONTV.indexOf(local.charAt(n + 1)) >= 0) {
258                        code.append('S');
259                        break; // CI,CE,CY -> S
260                    }
261                    code.append('K'); // default C -> K
262                    break;
263                case 'D':
264                    if (!isLastChar(wdsz, n + 1) && isNextChar(local, n, 'G') && FRONTV.indexOf(local.charAt(n + 2)) >= 0) { // DGE DGI DGY -> J
265                        code.append('J');
266                        n += 2;
267                    } else {
268                        code.append('T');
269                    }
270                    break;
271                case 'G': // GH silent at end or before consonant
272                    if (isLastChar(wdsz, n + 1) && isNextChar(local, n, 'H')) {
273                        break;
274                    }
275                    if (!isLastChar(wdsz, n + 1) && isNextChar(local, n, 'H') && !isVowel(local, n + 2)) {
276                        break;
277                    }
278                    if (n > 0 && (regionMatch(local, n, "GN") || regionMatch(local, n, "GNED"))) {
279                        break; // silent G
280                    }
281                    // NOTE: Given that duplicated chars are removed, I don't see how this can ever be true
282                    hard = isPreviousChar(local, n, 'G');
283                    if (!isLastChar(wdsz, n) && FRONTV.indexOf(local.charAt(n + 1)) >= 0 && !hard) {
284                        code.append('J');
285                    } else {
286                        code.append('K');
287                    }
288                    break;
289                case 'H':
290                    if (isLastChar(wdsz, n)) {
291                        break; // terminal H
292                    }
293                    if (n > 0 && VARSON.indexOf(local.charAt(n - 1)) >= 0) {
294                        break;
295                    }
296                    if (isVowel(local, n + 1)) {
297                        code.append('H'); // Hvowel
298                    }
299                    break;
300                case 'F':
301                case 'J':
302                case 'L':
303                case 'M':
304                case 'N':
305                case 'R':
306                    code.append(symb);
307                    break;
308                case 'K':
309                    if (n > 0) { // not initial
310                        if (!isPreviousChar(local, n, 'C')) {
311                            code.append(symb);
312                        }
313                    } else {
314                        code.append(symb); // initial K
315                    }
316                    break;
317                case 'P':
318                    if (isNextChar(local, n, 'H')) {
319                        // PH -> F
320                        code.append('F');
321                    } else {
322                        code.append(symb);
323                    }
324                    break;
325                case 'Q':
326                    code.append('K');
327                    break;
328                case 'S':
329                    if (regionMatch(local, n, "SH") || regionMatch(local, n, "SIO") || regionMatch(local, n, "SIA")) {
330                        code.append('X');
331                    } else {
332                        code.append('S');
333                    }
334                    break;
335                case 'T':
336                    if (regionMatch(local, n, "TIA") || regionMatch(local, n, "TIO")) {
337                        code.append('X');
338                        break;
339                    }
340                    if (regionMatch(local, n, "TCH")) {
341                        // Silent if in "TCH"
342                        break;
343                    }
344                    // substitute numeral 0 for TH (resembles theta after all)
345                    if (regionMatch(local, n, "TH")) {
346                        code.append('0');
347                    } else {
348                        code.append('T');
349                    }
350                    break;
351                case 'V':
352                    code.append('F');
353                    break;
354                case 'W':
355                case 'Y': // silent if not followed by vowel
356                    if (!isLastChar(wdsz, n) && isVowel(local, n + 1)) {
357                        code.append(symb);
358                    }
359                    break;
360                case 'X':
361                    code.append('K');
362                    code.append('S');
363                    break;
364                case 'Z':
365                    code.append('S');
366                    break;
367                default:
368                    // do nothing
369                    break;
370                } // end switch
371            } // end else from symb != 'C'
372            n++;
373            if (code.length() > getMaxCodeLen()) {
374                code.setLength(getMaxCodeLen());
375            }
376        }
377        return code.toString();
378    }
379
380    private boolean regionMatch(final StringBuilder string, final int index, final String test) {
381        boolean matches = false;
382        if (index >= 0 && index + test.length() - 1 < string.length()) {
383            final String substring = string.substring(index, index + test.length());
384            matches = substring.equals(test);
385        }
386        return matches;
387    }
388
389    /**
390     * Sets the maxCodeLen.
391     *
392     * @param maxCodeLen The maxCodeLen to set.
393     */
394    public void setMaxCodeLen(final int maxCodeLen) {
395        this.maxCodeLen = maxCodeLen;
396    }
397
398}