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.queue;
018
019import java.io.IOException;
020import java.io.ObjectInputStream;
021import java.io.ObjectOutputStream;
022import java.util.Collection;
023import java.util.Iterator;
024import java.util.Queue;
025import java.util.function.Predicate;
026
027import org.apache.commons.collections4.Unmodifiable;
028import org.apache.commons.collections4.iterators.UnmodifiableIterator;
029
030/**
031 * Decorates another {@link Queue} to ensure it can't be altered.
032 * <p>
033 * Attempts to modify it will result in an UnsupportedOperationException.
034 * </p>
035 *
036 * @param <E> The type of elements held in this queue
037 * @since 4.0
038 */
039public final class UnmodifiableQueue<E>
040        extends AbstractQueueDecorator<E>
041        implements Unmodifiable {
042
043    /** Serialization version */
044    private static final long serialVersionUID = 1832948656215393357L;
045
046    /**
047     * Factory method to create an unmodifiable queue.
048     * <p>
049     * If the queue passed in is already unmodifiable, it is returned.
050     *
051     * @param <E> The type of the elements in the queue
052     * @param queue  The queue to decorate, must not be null
053     * @return An unmodifiable Queue
054     * @throws NullPointerException if queue is null
055     */
056    public static <E> Queue<E> unmodifiableQueue(final Queue<? extends E> queue) {
057        if (queue instanceof Unmodifiable) {
058            @SuppressWarnings("unchecked") // safe to upcast
059            final Queue<E> tmpQueue = (Queue<E>) queue;
060            return tmpQueue;
061        }
062        return new UnmodifiableQueue<>(queue);
063    }
064
065    /**
066     * Constructor that wraps (not copies).
067     *
068     * @param queue  The queue to decorate, must not be null
069     * @throws NullPointerException if queue is null
070     */
071    @SuppressWarnings("unchecked") // safe to upcast
072    private UnmodifiableQueue(final Queue<? extends E> queue) {
073        super((Queue<E>) queue);
074    }
075
076    /**
077     * Always throws {@link UnsupportedOperationException}.
078     *
079     * @param object Ignored.
080     * @throws UnsupportedOperationException Always thrown.
081     */
082    @Override
083    public boolean add(final Object object) {
084        throw new UnsupportedOperationException();
085    }
086
087    /**
088     * Always throws {@link UnsupportedOperationException}.
089     *
090     * @param coll Ignored.
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 obj Ignored.
117     * @throws UnsupportedOperationException Always thrown.
118     */
119    @Override
120    public boolean offer(final E obj) {
121        throw new UnsupportedOperationException();
122    }
123
124    /**
125     * Always throws {@link UnsupportedOperationException}.
126     *
127     * @throws UnsupportedOperationException Always thrown.
128     */
129    @Override
130    public E poll() {
131        throw new UnsupportedOperationException();
132    }
133
134    /**
135     * Deserializes the collection in using a custom routine.
136     *
137     * @param in  The input stream
138     * @throws IOException Thrown if an I/O error occurs while reading from the input stream
139     * @throws ClassNotFoundException if the class of a serialized object cannot be found
140     */
141    @SuppressWarnings("unchecked")
142    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
143        in.defaultReadObject();
144        setCollection((Collection<E>) in.readObject());
145    }
146
147    /**
148     * Always throws {@link UnsupportedOperationException}.
149     *
150     * @throws UnsupportedOperationException Always thrown.
151     */
152    @Override
153    public E remove() {
154        throw new UnsupportedOperationException();
155    }
156
157    /**
158     * Always throws {@link UnsupportedOperationException}.
159     *
160     * @param object Ignored.
161     * @throws UnsupportedOperationException Always thrown.
162     */
163    @Override
164    public boolean remove(final Object object) {
165        throw new UnsupportedOperationException();
166    }
167
168    /**
169     * Always throws {@link UnsupportedOperationException}.
170     *
171     * @param coll Ignored.
172     * @throws UnsupportedOperationException Always thrown.
173     */
174    @Override
175    public boolean removeAll(final Collection<?> coll) {
176        throw new UnsupportedOperationException();
177    }
178
179    /**
180     * Always throws {@link UnsupportedOperationException}.
181     *
182     * @param filter Ignored.
183     * @throws UnsupportedOperationException Always thrown.
184     * @since 4.4
185     */
186    @Override
187    public boolean removeIf(final Predicate<? super E> filter) {
188        throw new UnsupportedOperationException();
189    }
190
191    /**
192     * Always throws {@link UnsupportedOperationException}.
193     *
194     * @param coll Ignored.
195     * @throws UnsupportedOperationException Always thrown.
196     */
197    @Override
198    public boolean retainAll(final Collection<?> coll) {
199        throw new UnsupportedOperationException();
200    }
201
202    /**
203     * Serializes this object to an ObjectOutputStream.
204     *
205     * @param out The target ObjectOutputStream.
206     * @throws IOException thrown when an I/O errors occur writing to the target stream.
207     */
208    private void writeObject(final ObjectOutputStream out) throws IOException {
209        out.defaultWriteObject();
210        out.writeObject(decorated());
211    }
212
213}