Returns the iterator's n:th item from the end of the iteration. - Java Collection Framework

Java examples for Collection Framework:Iterator

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Description

Returns the iterator's n:th item from the end of the iteration.

Demo Code

/**/*w  w w .j  av  a  2 s .  co m*/
 * 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.java2s;

import java.util.ArrayDeque;

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.
     */
    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;
    }

    /**
     * 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 iterable the {@link Iterable} to get elements from.
     * @param countFromEnd 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(Iterable<T> iterable, int countFromEnd) {
        return fromEndOrNull(iterable.iterator(), countFromEnd);
    }
}

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