    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 *      https://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}