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 */
032public class EmptyIterator<E> extends AbstractEmptyIterator<E> implements ResettableIterator<E> {
033
034    /**
035     * Singleton instance of the iterator.
036     * @since 3.1
037     */
038    @SuppressWarnings("rawtypes")
039    public static final ResettableIterator RESETTABLE_INSTANCE = new EmptyIterator<>();
040
041    /**
042     * Singleton instance of the iterator.
043     * @since 2.1.1 and 3.1
044     */
045    @SuppressWarnings("rawtypes")
046    public static final Iterator INSTANCE = RESETTABLE_INSTANCE;
047
048    /**
049     * Get a typed resettable empty iterator instance.
050     * @param <E> the element type
051     * @return ResettableIterator&lt;E&gt;
052     */
053    @SuppressWarnings("unchecked")
054    public static <E> ResettableIterator<E> resettableEmptyIterator() {
055        return RESETTABLE_INSTANCE;
056    }
057
058    /**
059     * Get a typed empty iterator instance.
060     * @param <E> the element type
061     * @return Iterator&lt;E&gt;
062     */
063    @SuppressWarnings("unchecked")
064    public static <E> Iterator<E> emptyIterator() {
065        return INSTANCE;
066    }
067
068    /**
069     * Constructor.
070     */
071    protected EmptyIterator() {
072        super();
073    }
074
075}