    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 *      http://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 */
    017package org.apache.commons.text.similarity;
    018
    019/**
    020 * The hamming distance between two strings of equal length is the number of
    021 * positions at which the corresponding symbols are different.
    022 *
    023 * <p>
    024 * For further explanation about the Hamming Distance, take a look at its
    025 * Wikipedia page at http://en.wikipedia.org/wiki/Hamming_distance.
    026 * </p>
    027 *
    028 * @since 1.0
    029 */
    030public class HammingDistance implements EditDistance<Integer> {
    031
    032    /**
    033     * Find the Hamming Distance between two strings with the same
    034     * length.
    035     *
    036     * <p>The distance starts with zero, and for each occurrence of a
    037     * different character in either String, it increments the distance
    038     * by 1, and finally return its value.</p>
    039     *
    040     * <p>Since the Hamming Distance can only be calculated between strings of equal length, input of different lengths
    041     * will throw IllegalArgumentException</p>
    042     *
    043     * <pre>
    044     * distance.apply("", "")               = 0
    045     * distance.apply("pappa", "pappa")     = 0
    046     * distance.apply("1011101", "1011111") = 1
    047     * distance.apply("ATCG", "ACCC")       = 2
    048     * distance.apply("karolin", "kerstin"  = 3
    049     * </pre>
    050     *
    051     * @param left the first CharSequence, must not be null
    052     * @param right the second CharSequence, must not be null
    053     * @return distance
    054     * @throws IllegalArgumentException if either input is {@code null} or
    055     *             if they do not have the same length
    056     */
    057    @Override
    058    public Integer apply(final CharSequence left, final CharSequence right) {
    059        if (left == null || right == null) {
    060            throw new IllegalArgumentException("Strings must not be null");
    061        }
    062
    063        if (left.length() != right.length()) {
    064            throw new IllegalArgumentException("Strings must have the same length");
    065        }
    066
    067        int distance = 0;
    068
    069        for (int i = 0; i < left.length(); i++) {
    070            if (left.charAt(i) != right.charAt(i)) {
    071                distance++;
    072            }
    073        }
    074
    075        return distance;
    076    }
    077
    078}