Java tutorial
//package com.java2s; /** * Copyright (C) 2012-2015 52North Initiative for Geospatial Open Source * Software GmbH * * This program is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 as published * by the Free Software Foundation. * * If the program is linked with libraries which are licensed under one of * the following licenses, the combination of the program with the linked * library is not considered a "derivative work" of the program: * * - Apache License, version 2.0 * - Apache Software License, version 1.0 * - GNU Lesser General Public License, version 3 * - Mozilla Public License, versions 1.0, 1.1 and 2.0 * - Common Development and Distribution License (CDDL), version 1.0 * * Therefore the distribution of the program linked with libraries licensed * under the aforementioned licenses, is permitted by the copyright holders * if the distribution is compliant with both the GNU General Public * License version 2 and the aforementioned licenses. * * This program is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General * Public License for more details. */ import static java.util.stream.Collectors.joining; import java.util.Arrays; import java.util.Collection; import java.util.Collections; import java.util.Map; import java.util.Map.Entry; import java.util.Optional; import java.util.stream.Collectors; public class Main { public static String collectionToString(Collection<?> collection) { return collection.stream().map(String::valueOf).collect(joining(",", "(", ")")); } /** * @param entries * the <i>final</i> set of entries to add to the newly created * <i>unmodifiable</i> map * @return an <i>unmodifiable</i> map with all given entries */ @SafeVarargs public static <K, V> Map<K, V> map(Entry<K, V>... entries) { return Collections .unmodifiableMap(Arrays.stream(entries).collect(Collectors.toMap(Entry::getKey, Entry::getValue))); } /** * @param <K> the key type * @param <V> the value type * @param m the map * @return an <b>UNMODIFIABLE</b> Map<K, V> */ public static <K, V> Map<K, V> unmodifiableMap(Map<? extends K, ? extends V> m) { return Optional.ofNullable(m).map(Collections::unmodifiableMap).orElseGet(Collections::emptyMap); } }