Java tutorial
//package com.java2s; /** * 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. */ import java.util.ArrayList; import java.util.List; import java.util.Map; public class Main { /** * Sets the value of the entry in the map for the given key, though if the * map already contains a value for the given key then the value is appended * to a list of values. * * @param map the map to add the entry to * @param key the key in the map * @param value the value to put in the map */ @SuppressWarnings("unchecked") public static void appendValue(Map<String, Object> map, String key, Object value) { Object oldValue = map.get(key); if (oldValue != null) { List<Object> list; if (oldValue instanceof List) { list = (List<Object>) oldValue; } else { list = new ArrayList<Object>(); list.add(oldValue); // replace old entry with list map.remove(key); map.put(key, list); } list.add(value); } else { map.put(key, value); } } }