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}.
029 * </p>
030 *
031 * @param <E> the type of elements returned by this iterator.
032 * @since 2.1.1 and 3.1
033 */
034public class EmptyIterator<E> extends AbstractEmptyIterator<E> {
035
036    /**
037     * Singleton instance of the iterator.
038     *
039     * @since 3.1
040     */
041    @SuppressWarnings("rawtypes")
042    public static final ResettableIterator RESETTABLE_INSTANCE = new EmptyIterator<>();
043
044    /**
045     * Singleton instance of the iterator.
046     *
047     * @since 2.1.1 and 3.1
048     */
049    @SuppressWarnings("rawtypes")
050    public static final Iterator INSTANCE = RESETTABLE_INSTANCE;
051
052    /**
053     * Gets a typed empty iterator instance.
054     *
055     * @param <E> the element type
056     * @return Iterator&lt;E&gt;
057     */
058    public static <E> Iterator<E> emptyIterator() {
059        return INSTANCE;
060    }
061
062    /**
063     * Gets a typed resettable empty iterator instance.
064     *
065     * @param <E> the element type
066     * @return ResettableIterator&lt;E&gt;
067     */
068    public static <E> ResettableIterator<E> resettableEmptyIterator() {
069        return RESETTABLE_INSTANCE;
070    }
071
072    /**
073     * Constructs a new instance.
074     */
075    protected EmptyIterator() {
076    }
077
078}