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.collection;
18
19 import java.util.Collection;
20 import java.util.Iterator;
21 import java.util.function.Predicate;
22
23 import org.apache.commons.collections4.Unmodifiable;
24 import org.apache.commons.collections4.iterators.UnmodifiableIterator;
25
26 /**
27 * Decorates another {@link Collection} to ensure it can't be altered.
28 * <p>
29 * This class is Serializable from Commons Collections 3.1.
30 * </p>
31 * <p>
32 * Attempts to modify it will result in an UnsupportedOperationException.
33 * </p>
34 *
35 * @param <E> the type of the elements in the collection
36 * @since 3.0
37 */
38 public final class UnmodifiableCollection<E>
39 extends AbstractCollectionDecorator<E>
40 implements Unmodifiable {
41
42 /** Serialization version */
43 private static final long serialVersionUID = -239892006883819945L;
44
45 /**
46 * Factory method to create an unmodifiable collection.
47 * <p>
48 * If the collection passed in is already unmodifiable, it is returned.
49 *
50 * @param <T> the type of the elements in the collection
51 * @param coll the collection to decorate, must not be null
52 * @return an unmodifiable collection
53 * @throws NullPointerException if collection is null
54 * @since 4.0
55 */
56 public static <T> Collection<T> unmodifiableCollection(final Collection<? extends T> coll) {
57 if (coll instanceof Unmodifiable) {
58 @SuppressWarnings("unchecked") // safe to upcast
59 final Collection<T> tmpColl = (Collection<T>) coll;
60 return tmpColl;
61 }
62 return new UnmodifiableCollection<>(coll);
63 }
64
65 /**
66 * Constructor that wraps (not copies).
67 *
68 * @param coll the collection to decorate, must not be null
69 * @throws NullPointerException if collection is null
70 */
71 @SuppressWarnings("unchecked") // safe to upcast
72 private UnmodifiableCollection(final Collection<? extends E> coll) {
73 super((Collection<E>) coll);
74 }
75
76 @Override
77 public boolean add(final E object) {
78 throw new UnsupportedOperationException();
79 }
80
81 @Override
82 public boolean addAll(final Collection<? extends E> coll) {
83 throw new UnsupportedOperationException();
84 }
85
86 @Override
87 public void clear() {
88 throw new UnsupportedOperationException();
89 }
90
91 @Override
92 public Iterator<E> iterator() {
93 return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
94 }
95
96 @Override
97 public boolean remove(final Object object) {
98 throw new UnsupportedOperationException();
99 }
100
101 @Override
102 public boolean removeAll(final Collection<?> coll) {
103 throw new UnsupportedOperationException();
104 }
105
106 /**
107 * @since 4.4
108 */
109 @Override
110 public boolean removeIf(final Predicate<? super E> filter) {
111 throw new UnsupportedOperationException();
112 }
113
114 @Override
115 public boolean retainAll(final Collection<?> coll) {
116 throw new UnsupportedOperationException();
117 }
118
119 }