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<E> 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<E> 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}