Java tutorial
/* * 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.text.translate; import java.io.IOException; import java.io.Writer; import java.util.HashMap; import java.util.HashSet; /** * Translates a value using a lookup table. * * @since 1.0 */ public class LookupTranslator extends CharSequenceTranslator { private final HashMap<String, String> lookupMap; private final HashSet<Character> prefixSet; private final int shortest; private final int longest; /** * Define the lookup table to be used in translation * * Note that, as of Lang 3.1, the key to the lookup table is converted to a * java.lang.String. This is because we need the key to support hashCode and * equals(Object), allowing it to be the key for a HashMap. See LANG-882. * * @param lookup CharSequence[][] table of size [*][2] */ public LookupTranslator(final CharSequence[]... lookup) { lookupMap = new HashMap<>(); prefixSet = new HashSet<>(); int _shortest = Integer.MAX_VALUE; int _longest = 0; if (lookup != null) { for (final CharSequence[] seq : lookup) { this.lookupMap.put(seq[0].toString(), seq[1].toString()); this.prefixSet.add(seq[0].charAt(0)); final int sz = seq[0].length(); if (sz < _shortest) { _shortest = sz; } if (sz > _longest) { _longest = sz; } } } shortest = _shortest; longest = _longest; } /** * {@inheritDoc} */ @Override public int translate(final CharSequence input, final int index, final Writer out) throws IOException { // check if translation exists for the input at position index if (prefixSet.contains(input.charAt(index))) { int max = longest; if (index + longest > input.length()) { max = input.length() - index; } // implement greedy algorithm by trying maximum match first for (int i = max; i >= shortest; i--) { final CharSequence subSeq = input.subSequence(index, index + i); final String result = lookupMap.get(subSeq.toString()); if (result != null) { out.write(result); return i; } } } return 0; } }