返回迭代结束时迭代器的n:th项。
/** * 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.ArrayDeque; /* n o w j a v a . c o m */ import java.util.Deque; import java.util.Iterator; import java.util.NoSuchElementException; public class Main { /** * Returns the iterator's n:th item from the end of the iteration. * If the iterator has got less than n-1 items in it * {@link NoSuchElementException} is thrown. * * @param <T> the type of elements in {@code iterator}. * @param iterator the {@link Iterator} to get elements from. * @param n the n:th item from the end to get. * @return the iterator's n:th item from the end of the iteration. * @throws NoSuchElementException if the iterator contains less than n-1 items. *///nowjava - 时代Java public static <T> T fromEnd(Iterator<T> iterator, int n) { return assertNotNull(iterator, fromEndOrNull(iterator, n)); } /** * Returns the iterator's n:th item from the end of the iteration. * If the iterator has got less than n-1 items in it * {@link NoSuchElementException} is thrown. * * @param <T> the type of elements in {@code iterator}. * @param iterable the {@link Iterable} to get elements from. * @param n the n:th item from the end to get. * @return the iterator's n:th item from the end of the iteration. * @throws NoSuchElementException if the iterator contains less than n-1 items. */ public static <T> T fromEnd(Iterable<T> iterable, int n) { return fromEnd(iterable.iterator(), n); } private static <T> T assertNotNull(Iterator<T> iterator, T result) { if (result == null) { throw new NoSuchElementException("No element found in " + iterator); } return result; } /** * Returns the iterator's n:th item from the end of the iteration. * If the iterator has got less than n-1 items in it {@code null} is returned. * * @param <T> the type of elements in {@code iterator}. * @param iterator the {@link Iterator} to get elements from. * @param n the n:th item from the end to get. * @return the iterator's n:th item from the end of the iteration, * or {@code null} if the iterator doesn't contain that many items. */ public static <T> T fromEndOrNull(Iterator<T> iterator, int n) { Deque<T> trail = new ArrayDeque<T>(n); while (iterator.hasNext()) { if (trail.size() > n) { trail.removeLast(); } trail.addFirst(iterator.next()); } return trail.size() == n + 1 ? trail.getLast() : null; }