返回给定迭代器的第一个元素；如果未找到任何元素，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;/*时代Java 提供*/


import java.util.Iterator;


public class Main {

    /**

     * Returns the given iterator's first element or {@code null} if no

     * element found.

     * 

     * @param <T> the type of elements in {@code iterator}.

     * @param iterator the {@link Iterator} to get elements from.

     * @return the first element in the {@code iterator}, or {@code null} if no

     * element found.

     */

    public static <T> T firstOrNull(Iterator<T> iterator) {

        return iterator.hasNext() ? iterator.next() : null;

    }