1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.collections4.iterators;
18
19 import java.util.Iterator;
20
21 import org.apache.commons.collections4.ResettableIterator;
22
23 /**
24 * Provides an implementation of an empty iterator.
25 * <p>
26 * This class provides an implementation of an empty iterator.
27 * This class provides for binary compatibility between Commons Collections
28 * 2.1.1 and 3.1 due to issues with {@code IteratorUtils}.
29 *
30 * @param <E> the type of elements returned by this iterator.
31 * @since 2.1.1 and 3.1
32 */
33 public class EmptyIterator<E> extends AbstractEmptyIterator<E> implements ResettableIterator<E> {
34
35 /**
36 * Singleton instance of the iterator.
37 * @since 3.1
38 */
39 @SuppressWarnings("rawtypes")
40 public static final ResettableIterator RESETTABLE_INSTANCE = new EmptyIterator<>();
41
42 /**
43 * Singleton instance of the iterator.
44 * @since 2.1.1 and 3.1
45 */
46 @SuppressWarnings("rawtypes")
47 public static final Iterator INSTANCE = RESETTABLE_INSTANCE;
48
49 /**
50 * Gets a typed empty iterator instance.
51 * @param <E> the element type
52 * @return Iterator<E>
53 */
54 public static <E> Iterator<E> emptyIterator() {
55 return INSTANCE;
56 }
57
58 /**
59 * Gets a typed resettable empty iterator instance.
60 * @param <E> the element type
61 * @return ResettableIterator<E>
62 */
63 public static <E> ResettableIterator<E> resettableEmptyIterator() {
64 return RESETTABLE_INSTANCE;
65 }
66
67 /**
68 * Constructs a new instance.
69 */
70 protected EmptyIterator() {
71 }
72
73 }