返回给定迭代器的单个元素，如果找不到元素，则返回null。
/** * Copyright (c) 2002-2013 "Neo Technology," * Network Engine for Objects in Lund AB [http://neotechnology.com] * * This file is part of Neo4j. * * Neo4j is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * 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. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. */ //package com.nowjava; import java.util.Iterator; /** 来 自 n o w j a v a . c o m - 时 代 Java **/ import java.util.NoSuchElementException; public class Main { /** * Returns the given iterator's single element or {@code null} if no * element found. If there is more than one element in the iterator a * {@link NoSuchElementException} will be thrown. * * @param <T> the type of elements in {@code iterator}. * @param iterator the {@link Iterator} to get elements from. * @return the single element in {@code iterator}, or {@code null} if no * element found. * @throws {@link NoSuchElementException} if more than one element was * found. */ public static <T> T singleOrNull(Iterator<T> iterator) { T result = iterator.hasNext() ? iterator.next() : null; if (iterator.hasNext()) { throw new NoSuchElementException("More than one element in " + iterator + ". First element is '" + result + "' and the second element is '" + iterator.next() + "'"); } /* N o w J a v a . c o m 提供 */ return result; }