001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.collection;
018
019import java.util.Collection;
020import java.util.Iterator;
021import java.util.function.Predicate;
022
023import org.apache.commons.collections4.Unmodifiable;
024import org.apache.commons.collections4.iterators.UnmodifiableIterator;
025
026/**
027 * Decorates another {@link Collection} to ensure it can't be altered.
028 * <p>
029 * This class is Serializable from Commons Collections 3.1.
030 * </p>
031 * <p>
032 * Attempts to modify it will result in an UnsupportedOperationException.
033 * </p>
034 *
035 * @param <E> The type of the elements in the collection.
036 * @since 3.0
037 */
038public final class UnmodifiableCollection<E>
039        extends AbstractCollectionDecorator<E>
040        implements Unmodifiable {
041
042    /** Serialization version */
043    private static final long serialVersionUID = -239892006883819945L;
044
045    /**
046     * Creates an unmodifiable collection.
047     * <p>
048     * If the collection passed in is already unmodifiable, it is returned.
049     * </p>
050     *
051     * @param <T> The type of the elements in the collection.
052     * @param coll  The collection to decorate, must not be null.
053     * @return An unmodifiable collection.
054     * @throws NullPointerException if collection is null.
055     * @since 4.0
056     */
057    public static <T> Collection<T> unmodifiableCollection(final Collection<? extends T> coll) {
058        if (coll instanceof Unmodifiable) {
059            @SuppressWarnings("unchecked") // safe to upcast
060            final Collection<T> tmpColl = (Collection<T>) coll;
061            return tmpColl;
062        }
063        return new UnmodifiableCollection<>(coll);
064    }
065
066    /**
067     * Constructs and wraps (not copies).
068     *
069     * @param coll  The collection to decorate, must not be null.
070     * @throws NullPointerException if collection is null.
071     */
072    @SuppressWarnings("unchecked") // safe to upcast
073    private UnmodifiableCollection(final Collection<? extends E> coll) {
074        super((Collection<E>) coll);
075    }
076
077    /**
078     * Always throws {@link UnsupportedOperationException}.
079     *
080     * @param object Ignored.
081     * @throws UnsupportedOperationException Always thrown.
082     */
083    @Override
084    public boolean add(final E object) {
085        throw new UnsupportedOperationException();
086    }
087
088    /**
089     * Always throws {@link UnsupportedOperationException}.
090     *
091     * @throws UnsupportedOperationException Always thrown.
092     */
093    @Override
094    public boolean addAll(final Collection<? extends E> coll) {
095        throw new UnsupportedOperationException();
096    }
097
098    /**
099     * Always throws {@link UnsupportedOperationException}.
100     *
101     * @throws UnsupportedOperationException Always thrown.
102     */
103    @Override
104    public void clear() {
105        throw new UnsupportedOperationException();
106    }
107
108    @Override
109    public Iterator<E> iterator() {
110        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
111    }
112
113    /**
114     * Always throws {@link UnsupportedOperationException}.
115     *
116     * @param object Ignored.
117     * @throws UnsupportedOperationException Always thrown.
118     */
119    @Override
120    public boolean remove(final Object object) {
121        throw new UnsupportedOperationException();
122    }
123
124    /**
125     * Always throws {@link UnsupportedOperationException}.
126     *
127     * @param coll Ignored.
128     * @throws UnsupportedOperationException Always thrown.
129     */
130    @Override
131    public boolean removeAll(final Collection<?> coll) {
132        throw new UnsupportedOperationException();
133    }
134
135    /**
136     * Always throws {@link UnsupportedOperationException}.
137     *
138     * @param filter Ignored.
139     * @throws UnsupportedOperationException Always thrown.
140     * @since 4.4
141     */
142    @Override
143    public boolean removeIf(final Predicate<? super E> filter) {
144        throw new UnsupportedOperationException();
145    }
146
147    /**
148     * Always throws {@link UnsupportedOperationException}.
149     *
150     * @param coll Ignored.
151     * @throws UnsupportedOperationException Always thrown.
152     */
153    @Override
154    public boolean retainAll(final Collection<?> coll) {
155        throw new UnsupportedOperationException();
156    }
157
158}