    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}