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 * https://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 * Calling {@link #remove()} throws {@link UnsupportedOperationException}.
28 * </p>
29 *
30 * @param <E> The type of elements returned by this iterator.
31 * @param <T> The wrapped Iterator type.
32 * @since 3.0
33 */
34 public final class UnmodifiableIterator<E, T extends Iterator<? extends E>> implements Iterator<E>, Unmodifiable {
35
36 /**
37 * Decorates the specified iterator such that it cannot be modified.
38 * <p>
39 * If the iterator is already unmodifiable it is returned directly.
40 * </p>
41 *
42 * @param <E> the element type
43 * @param iterator The iterator to decorate
44 * @return A new unmodifiable iterator
45 * @throws NullPointerException if the iterator is null
46 */
47 public static <E> Iterator<E> unmodifiableIterator(final Iterator<? extends E> iterator) {
48 Objects.requireNonNull(iterator, "iterator");
49 if (iterator instanceof Unmodifiable) {
50 @SuppressWarnings("unchecked") // safe to upcast
51 final Iterator<E> tmpIterator = (Iterator<E>) iterator;
52 return tmpIterator;
53 }
54 return wrap(iterator);
55 }
56
57 static <E, T extends Iterator<? extends E>> UnmodifiableIterator<E, T> wrap(final T iterator) {
58 return new UnmodifiableIterator<>(iterator);
59 }
60
61 /**
62 * The decorated iterator.
63 */
64 private final T iterator;
65
66 /**
67 * Constructs a new instance.
68 *
69 * @param iterator The iterator to decorate.
70 */
71 private UnmodifiableIterator(final T iterator) {
72 this.iterator = iterator;
73 }
74
75 @Override
76 public boolean hasNext() {
77 return iterator.hasNext();
78 }
79
80 @Override
81 public E next() {
82 return iterator.next();
83 }
84
85 /**
86 * Always throws {@link UnsupportedOperationException}.
87 *
88 * @throws UnsupportedOperationException Always thrown.
89 */
90 // TODO This method can be removed in 5.0 since it's implemented as a default method in Iterator.
91 @Override
92 public void remove() {
93 throw new UnsupportedOperationException("remove");
94 }
95
96 T unwrap() {
97 return iterator;
98 }
99 }