Returns the given iterator's single element. - Java Collection Framework

Java examples for Collection Framework:Iterator

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Description

Returns the given iterator's single element.

Demo Code

/**//from   w  w  w. j a v 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.Iterator;

import java.util.NoSuchElementException;

public class Main {
    /**
     * Returns the given iterator's single element. If there are no elements
     * or 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 the {@code iterator}.
     * @throws {@link NoSuchElementException} if there isn't exactly one
     * element.
     */
    public static <T> T single(Iterator<T> iterator) {
        return assertNotNull(iterator, singleOrNull(iterator));
    }

    /**
     * Returns the given iterable's single element. If there are no elements
     * or more than one element in the iterable a {@link NoSuchElementException}
     * will be thrown.
     * 
     * @param <T> the type of elements in {@code iterable}.
     * @param iterable the {@link Iterable} to get elements from.
     * @return the single element in the {@code iterable}.
     * @throws {@link NoSuchElementException} if there isn't exactly one
     * element.
     */
    public static <T> T single(Iterable<T> iterable) {
        return single(iterable.iterator());
    }

    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 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()
                    + "'");
        }
        return result;
    }

    /**
     * Returns the given iterable's single element or {@code null} if no
     * element found. If there is more than one element in the iterable a
     * {@link NoSuchElementException} will be thrown.
     * 
     * @param <T> the type of elements in {@code iterable}.
     * @param iterable the {@link Iterable} to get elements from.
     * @return the single element in {@code iterable}, or {@code null} if no
     * element found.
     * @throws {@link NoSuchElementException} if more than one element was
     * found.
     */
    public static <T> T singleOrNull(Iterable<T> iterable) {
        return singleOrNull(iterable.iterator());
    }
}

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