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 *      http://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    @Override
077    public boolean add(final Object object) {
078        throw new UnsupportedOperationException();
079    }
080
081    @Override
082    public boolean addAll(final Collection<? extends E> coll) {
083        throw new UnsupportedOperationException();
084    }
085
086    @Override
087    public void clear() {
088        throw new UnsupportedOperationException();
089    }
090
091    @Override
092    public Iterator<E> iterator() {
093        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
094    }
095
096    @Override
097    public boolean offer(final E obj) {
098        throw new UnsupportedOperationException();
099    }
100
101    @Override
102    public E poll() {
103        throw new UnsupportedOperationException();
104    }
105
106    /**
107     * Deserializes the collection in using a custom routine.
108     *
109     * @param in  the input stream
110     * @throws IOException if an I/O error occurs while reading from the input stream
111     * @throws ClassNotFoundException if the class of a serialized object cannot be found
112     */
113    @SuppressWarnings("unchecked")
114    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
115        in.defaultReadObject();
116        setCollection((Collection<E>) in.readObject());
117    }
118
119    @Override
120    public E remove() {
121        throw new UnsupportedOperationException();
122    }
123
124    @Override
125    public boolean remove(final Object object) {
126        throw new UnsupportedOperationException();
127    }
128
129    @Override
130    public boolean removeAll(final Collection<?> coll) {
131        throw new UnsupportedOperationException();
132    }
133
134    /**
135     * @since 4.4
136     */
137    @Override
138    public boolean removeIf(final Predicate<? super E> filter) {
139        throw new UnsupportedOperationException();
140    }
141
142    @Override
143    public boolean retainAll(final Collection<?> coll) {
144        throw new UnsupportedOperationException();
145    }
146
147    /**
148     * Serializes this object to an ObjectOutputStream.
149     *
150     * @param out the target ObjectOutputStream.
151     * @throws IOException thrown when an I/O errors occur writing to the target stream.
152     */
153    private void writeObject(final ObjectOutputStream out) throws IOException {
154        out.defaultWriteObject();
155        out.writeObject(decorated());
156    }
157
158}