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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</code>.
29   *
30   * @since 2.1.1 and 3.1
31   */
32  public class EmptyIterator<E> extends AbstractEmptyIterator<E> implements ResettableIterator<E> {
33  
34      /**
35       * Singleton instance of the iterator.
36       * @since 3.1
37       */
38      @SuppressWarnings("rawtypes")
39      public static final ResettableIterator RESETTABLE_INSTANCE = new EmptyIterator<>();
40  
41      /**
42       * Singleton instance of the iterator.
43       * @since 2.1.1 and 3.1
44       */
45      @SuppressWarnings("rawtypes")
46      public static final Iterator INSTANCE = RESETTABLE_INSTANCE;
47  
48      /**
49       * Get a typed resettable empty iterator instance.
50       * @param <E> the element type
51       * @return ResettableIterator&lt;E&gt;
52       */
53      public static <E> ResettableIterator<E> resettableEmptyIterator() {
54          return RESETTABLE_INSTANCE;
55      }
56  
57      /**
58       * Get a typed empty iterator instance.
59       * @param <E> the element type
60       * @return Iterator&lt;E&gt;
61       */
62      public static <E> Iterator<E> emptyIterator() {
63          return INSTANCE;
64      }
65  
66      /**
67       * Constructor.
68       */
69      protected EmptyIterator() {
70          super();
71      }
72  
73  }