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.toMap; import java.util.LinkedHashMap; import java.util.Map.Entry; import java.util.function.BinaryOperator; import java.util.stream.Collector; public class Main { private static <K, V> Collector<Entry<K, V>, ?, LinkedHashMap<K, V>> toLinkedHashMap() { return toMap(Entry::getKey, Entry::getValue, throwingMerger(), LinkedHashMap::new); } private static <T> BinaryOperator<T> throwingMerger() { return (u, v) -> { throw new IllegalStateException(String.format("Duplicate key %s", u)); }; } }