    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 *
    030 * @param <E> the type of elements returned by this iterator.
    031 * @since 2.1.1 and 3.1
    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<>();
    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     * Gets a typed empty iterator instance.
    051     * @param <E> the element type
    052     * @return Iterator&lt;E&gt;
    053     */
    054    public static <E> Iterator<E> emptyIterator() {
    055        return INSTANCE;
    056    }
    057
    058    /**
    059     * Gets a typed resettable empty iterator instance.
    060     * @param <E> the element type
    061     * @return ResettableIterator&lt;E&gt;
    062     */
    063    public static <E> ResettableIterator<E> resettableEmptyIterator() {
    064        return RESETTABLE_INSTANCE;
    065    }
    066
    067    /**
    068     * Constructs a new instance.
    069     */
    070    protected EmptyIterator() {
    071    }
    072
    073}