001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.iterators;
018
019import java.util.Iterator;
020
021import org.apache.commons.collections4.ResettableIterator;
022
023/**
024 * Provides an implementation of an empty iterator.
025 * <p>
026 * This class provides an implementation of an empty iterator.
027 * This class provides for binary compatibility between Commons Collections
028 * 2.1.1 and 3.1 due to issues with <code>IteratorUtils</code>.
029 *
030 * @since 2.1.1 and 3.1
031 * @version $Id: EmptyIterator.html 972421 2015-11-14 20:00:04Z tn $
032 */
033public class EmptyIterator<E> extends AbstractEmptyIterator<E> implements ResettableIterator<E> {
034
035    /**
036     * Singleton instance of the iterator.
037     * @since 3.1
038     */
039    @SuppressWarnings("rawtypes")
040    public static final ResettableIterator RESETTABLE_INSTANCE = new EmptyIterator<Object>();
041
042    /**
043     * Singleton instance of the iterator.
044     * @since 2.1.1 and 3.1
045     */
046    @SuppressWarnings("rawtypes")
047    public static final Iterator INSTANCE = RESETTABLE_INSTANCE;
048
049    /**
050     * Get a typed resettable empty iterator instance.
051     * @param <E> the element type
052     * @return ResettableIterator<E>
053     */
054    @SuppressWarnings("unchecked")
055    public static <E> ResettableIterator<E> resettableEmptyIterator() {
056        return (ResettableIterator<E>) RESETTABLE_INSTANCE;
057    }
058
059    /**
060     * Get a typed empty iterator instance.
061     * @param <E> the element type
062     * @return Iterator<E>
063     */
064    @SuppressWarnings("unchecked")
065    public static <E> Iterator<E> emptyIterator() {
066        return (Iterator<E>) INSTANCE;
067    }
068
069    /**
070     * Constructor.
071     */
072    protected EmptyIterator() {
073        super();
074    }
075
076}