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 import java.util.Objects;
21
22 import org.apache.commons.collections4.Unmodifiable;
23
24 /**
25 * Decorates an iterator such that it cannot be modified.
26 * <p>
27 * Attempts to modify it will result in an UnsupportedOperationException.
28 * </p>
29 *
30 * @param <E> the type of elements returned by this iterator.
31 * @since 3.0
32 */
33 public final class UnmodifiableIterator<E> implements Iterator<E>, Unmodifiable {
34
35 /**
36 * Decorates the specified iterator such that it cannot be modified.
37 * <p>
38 * If the iterator is already unmodifiable it is returned directly.
39 *
40 * @param <E> the element type
41 * @param iterator the iterator to decorate
42 * @return a new unmodifiable iterator
43 * @throws NullPointerException if the iterator is null
44 */
45 public static <E> Iterator<E> unmodifiableIterator(final Iterator<? extends E> iterator) {
46 Objects.requireNonNull(iterator, "iterator");
47 if (iterator instanceof Unmodifiable) {
48 @SuppressWarnings("unchecked") // safe to upcast
49 final Iterator<E> tmpIterator = (Iterator<E>) iterator;
50 return tmpIterator;
51 }
52 return new UnmodifiableIterator<>(iterator);
53 }
54
55 /** The iterator being decorated */
56 private final Iterator<? extends E> iterator;
57
58 /**
59 * Constructs a new instance.
60 *
61 * @param iterator the iterator to decorate
62 */
63 private UnmodifiableIterator(final Iterator<? extends E> iterator) {
64 this.iterator = iterator;
65 }
66
67 @Override
68 public boolean hasNext() {
69 return iterator.hasNext();
70 }
71
72 @Override
73 public E next() {
74 return iterator.next();
75 }
76
77 @Override
78 public void remove() {
79 throw new UnsupportedOperationException("remove() is not supported");
80 }
81
82 }