    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    /**
    067     * Constructor that wraps (not copies).
    068     *
    069     * @param queue  the queue to decorate, must not be null
    070     * @throws NullPointerException if queue is null
    071     */
    072    @SuppressWarnings("unchecked") // safe to upcast
    073    private UnmodifiableQueue(final Queue<? extends E> queue) {
    074        super((Queue<E>) queue);
    075    }
    076
    077    //-----------------------------------------------------------------------
    078    /**
    079     * Write the collection out using a custom routine.
    080     *
    081     * @param out  the output stream
    082     * @throws IOException if an I/O error occurs while writing to the output stream
    083     */
    084    private void writeObject(final ObjectOutputStream out) throws IOException {
    085        out.defaultWriteObject();
    086        out.writeObject(decorated());
    087    }
    088
    089    /**
    090     * Read the collection in using a custom routine.
    091     *
    092     * @param in  the input stream
    093     * @throws IOException if an I/O error occurs while reading from the input stream
    094     * @throws ClassNotFoundException if the class of a serialized object can not be found
    095     */
    096    @SuppressWarnings("unchecked")
    097    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    098        in.defaultReadObject();
    099        setCollection((Collection<E>) in.readObject());
    100    }
    101
    102    //-----------------------------------------------------------------------
    103    @Override
    104    public Iterator<E> iterator() {
    105        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
    106    }
    107
    108    @Override
    109    public boolean add(final Object object) {
    110        throw new UnsupportedOperationException();
    111    }
    112
    113    @Override
    114    public boolean addAll(final Collection<? extends E> coll) {
    115        throw new UnsupportedOperationException();
    116    }
    117
    118    @Override
    119    public void clear() {
    120        throw new UnsupportedOperationException();
    121    }
    122
    123    @Override
    124    public boolean remove(final Object object) {
    125        throw new UnsupportedOperationException();
    126    }
    127
    128    /**
    129     * @since 4.4
    130     */
    131    @Override
    132    public boolean removeIf(Predicate<? super E> filter) {
    133        throw new UnsupportedOperationException();
    134    }
    135
    136    @Override
    137    public boolean removeAll(final Collection<?> coll) {
    138        throw new UnsupportedOperationException();
    139    }
    140
    141    @Override
    142    public boolean retainAll(final Collection<?> coll) {
    143        throw new UnsupportedOperationException();
    144    }
    145
    146    //-----------------------------------------------------------------------
    147
    148    @Override
    149    public boolean offer(final E obj) {
    150        throw new UnsupportedOperationException();
    151    }
    152
    153    @Override
    154    public E poll() {
    155        throw new UnsupportedOperationException();
    156    }
    157
    158    @Override
    159    public E remove() {
    160        throw new UnsupportedOperationException();
    161    }
    162
    163}