Java tutorial
//package com.java2s; /* * Copyright 2015-2018 52North Initiative for Geospatial Open Source * Software GmbH * * Licensed 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.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(Collectors.joining(",", "(", ")")); } /** * @param entries * the <i>final</i> set of entries to add to the newly created * <i>unmodifiable</i> map * @param <K> the key type * @param <V> the value type * * @return an <i>unmodifiable</i> map with all given entries */ @SafeVarargs @SuppressWarnings("varargs") 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<? extends K, ? extends V> unmodifiableMap(Map<? extends K, ? extends V> m) { return Optional.ofNullable(m).map(Collections::unmodifiableMap).orElseGet(Collections::emptyMap); } }