Soundex.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 Soundex value. Soundex is an encoding used to relate similar names, but can also be used as a
* general purpose scheme to find word with similar phonemes.
*
* <p>This class is thread-safe.
* Although not strictly immutable, the mutable fields are not actually used.</p>
*/
public class Soundex implements StringEncoder {
/**
* The marker character used to indicate a silent (ignored) character.
* These are ignored except when they appear as the first character.
* <p>
* Note: the {@link #US_ENGLISH_MAPPING_STRING} does not use this mechanism
* because changing it might break existing code. Mappings that don't contain
* a silent marker code are treated as though H and W are silent.
* </p>
* <p>
* To override this, use the {@link #Soundex(String, boolean)} constructor.
* </p>
*
* @since 1.11
*/
public static final char SILENT_MARKER = '-';
/**
* This is a default mapping of the 26 letters used in US English. A value of {@code 0} for a letter position
* means do not encode, but treat as a separator when it occurs between consonants with the same code.
* <p>
* (This constant is provided as both an implementation convenience and to allow Javadoc to pick
* up the value for the constant values page.)
* </p>
* <p>
* <b>Note that letters H and W are treated specially.</b>
* They are ignored (after the first letter) and don't act as separators
* between consonants with the same code.
* </p>
*/
public static final String US_ENGLISH_MAPPING_STRING = "01230120022455012623010202";
/**
* This is a default mapping of the 26 letters used in US English. A value of {@code 0} for a letter position
* means do not encode.
*
* @see Soundex#Soundex(char[])
*/
private static final char[] US_ENGLISH_MAPPING = US_ENGLISH_MAPPING_STRING.toCharArray();
/**
* An instance of Soundex using the US_ENGLISH_MAPPING mapping.
* This treats H and W as silent letters.
* Apart from when they appear as the first letter, they are ignored.
* They don't act as separators between duplicate codes.
*
* @see #US_ENGLISH_MAPPING_STRING
*/
public static final Soundex US_ENGLISH = new Soundex();
/**
* An instance of Soundex using the Simplified Soundex mapping, as described here:
* http://west-penwith.org.uk/misc/soundex.htm
* <p>
* This treats H and W the same as vowels (AEIOUY).
* Such letters aren't encoded (after the first), but they do
* act as separators when dropping duplicate codes.
* The mapping is otherwise the same as for {@link #US_ENGLISH}
* </p>
*
* @since 1.11
*/
public static final Soundex US_ENGLISH_SIMPLIFIED = new Soundex(US_ENGLISH_MAPPING_STRING, false);
/**
* An instance of Soundex using the mapping as per the Genealogy site:
* http://www.genealogy.com/articles/research/00000060.html
* <p>
* This treats vowels (AEIOUY), H and W as silent letters.
* Such letters are ignored (after the first) and do not
* act as separators when dropping duplicate codes.
* </p>
* <p>
* The codes for consonants are otherwise the same as for
* {@link #US_ENGLISH_MAPPING_STRING} and {@link #US_ENGLISH_SIMPLIFIED}
* </p>
*
* @since 1.11
*/
public static final Soundex US_ENGLISH_GENEALOGY = new Soundex("-123-12--22455-12623-1-2-2");
// ABCDEFGHIJKLMNOPQRSTUVWXYZ
/**
* The maximum length of a Soundex code - Soundex codes are only four characters by definition.
*
* @deprecated This feature is not needed since the encoding size must be constant. Will be removed in 2.0.
*/
@Deprecated
private int maxLength = 4;
/**
* Every letter of the alphabet is "mapped" to a numerical value. This char array holds the values to which each
* letter is mapped. This implementation contains a default map for US_ENGLISH
*/
private final char[] soundexMapping;
/**
* Should H and W be treated specially?
* <p>
* In versions of the code prior to 1.11,
* the code always treated H and W as silent (ignored) letters.
* If this field is false, H and W are no longer special-cased.
* </p>
*/
private final boolean specialCaseHW;
/**
* Creates an instance using US_ENGLISH_MAPPING
*
* @see Soundex#Soundex(char[])
* @see Soundex#US_ENGLISH_MAPPING_STRING
*/
public Soundex() {
this.soundexMapping = US_ENGLISH_MAPPING;
this.specialCaseHW = true;
}
/**
* Creates a soundex instance using the given mapping. This constructor can be used to provide an internationalized
* mapping for a non-Western character set.
* <p>
* Every letter of the alphabet is "mapped" to a numerical value. This char array holds the values to which each
* letter is mapped. This implementation contains a default map for US_ENGLISH
* </p>
* <p>
* If the mapping contains an instance of {@link #SILENT_MARKER} then H and W are not given special treatment
* </p>
*
* @param mapping
* Mapping array to use when finding the corresponding code for a given character
*/
public Soundex(final char[] mapping) {
this.soundexMapping = mapping.clone();
this.specialCaseHW = !hasMarker(this.soundexMapping);
}
/**
* Creates a refined soundex instance using a custom mapping. This constructor can be used to customize the mapping,
* and/or possibly provide an internationalized mapping for a non-Western character set.
* <p>
* If the mapping contains an instance of {@link #SILENT_MARKER} then H and W are not given special treatment
* </p>
*
* @param mapping
* Mapping string to use when finding the corresponding code for a given character
* @since 1.4
*/
public Soundex(final String mapping) {
this.soundexMapping = mapping.toCharArray();
this.specialCaseHW = !hasMarker(this.soundexMapping);
}
/**
* Creates a refined soundex instance using a custom mapping. This constructor can be used to customize the mapping,
* and/or possibly provide an internationalized mapping for a non-Western character set.
*
* @param mapping
* Mapping string to use when finding the corresponding code for a given character
* @param specialCaseHW if true, then
* @since 1.11
*/
public Soundex(final String mapping, final boolean specialCaseHW) {
this.soundexMapping = mapping.toCharArray();
this.specialCaseHW = specialCaseHW;
}
/**
* Encodes the Strings and returns the number of characters in the two encoded Strings that are the same. This
* return value ranges from 0 through 4: 0 indicates little or no similarity, and 4 indicates strong similarity or
* identical values.
*
* @param s1
* A String that will be encoded and compared.
* @param s2
* A String that will be encoded and compared.
* @return The number of characters in the two encoded Strings that are the same from 0 to 4.
*
* @see SoundexUtils#difference(StringEncoder,String,String)
* @see <a href="https://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts_de-dz_8co5.asp"> MS
* T-SQL DIFFERENCE</a>
*
* @throws EncoderException
* if an error occurs encoding one of the strings
* @since 1.3
*/
public int difference(final String s1, final String s2) throws EncoderException {
return SoundexUtils.difference(this, s1, s2);
}
/**
* Encodes an Object using the soundex 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 soundex code which corresponds to the String
* supplied.
* @throws EncoderException
* if the parameter supplied is not of type {@link String}
* @throws IllegalArgumentException
* if a character is not mapped
*/
@Override
public Object encode(final Object obj) throws EncoderException {
if (!(obj instanceof String)) {
throw new EncoderException("Parameter supplied to Soundex encode is not of type java.lang.String");
}
return soundex((String) obj);
}
/**
* Encodes a String using the soundex algorithm.
*
* @param str
* A String object to encode
* @return A Soundex code corresponding to the String supplied
* @throws IllegalArgumentException
* if a character is not mapped
*/
@Override
public String encode(final String str) {
return soundex(str);
}
/**
* Returns the maxLength. Standard Soundex
*
* @deprecated This feature is not needed since the encoding size must be constant. Will be removed in 2.0.
* @return int
*/
@Deprecated
public int getMaxLength() {
return this.maxLength;
}
private boolean hasMarker(final char[] mapping) {
for (final char ch : mapping) {
if (ch == SILENT_MARKER) {
return true;
}
}
return false;
}
/**
* Maps the given upper-case character to its Soundex code.
*
* @param ch
* An upper-case character.
* @return A Soundex code.
* @throws IllegalArgumentException
* Thrown if {@code ch} is not mapped.
*/
private char map(final char ch) {
final int index = ch - 'A';
if (index < 0 || index >= this.soundexMapping.length) {
throw new IllegalArgumentException("The character is not mapped: " + ch + " (index=" + index + ")");
}
return this.soundexMapping[index];
}
/**
* Sets the maxLength.
*
* @deprecated This feature is not needed since the encoding size must be constant. Will be removed in 2.0.
* @param maxLength
* The maxLength to set
*/
@Deprecated
public void setMaxLength(final int maxLength) {
this.maxLength = maxLength;
}
/**
* Retrieves the Soundex code for a given String object.
*
* @param str
* String to encode using the Soundex algorithm
* @return A soundex code for the String supplied
* @throws IllegalArgumentException
* if a character is not mapped
*/
public String soundex(String str) {
if (str == null) {
return null;
}
str = SoundexUtils.clean(str);
if (str.isEmpty()) {
return str;
}
final char[] out = { '0', '0', '0', '0' };
int count = 0;
final char first = str.charAt(0);
out[count++] = first;
char lastDigit = map(first); // previous digit
for (int i = 1; i < str.length() && count < out.length; i++) {
final char ch = str.charAt(i);
if (this.specialCaseHW && (ch == 'H' || ch == 'W')) { // these are ignored completely
continue;
}
final char digit = map(ch);
if (digit == SILENT_MARKER) {
continue;
}
if (digit != '0' && digit != lastDigit) { // don't store vowels or repeats
out[count++] = digit;
}
lastDigit = digit;
}
return new String(out);
}
}