    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;
    025
    026import org.apache.commons.collections4.Unmodifiable;
    027import org.apache.commons.collections4.iterators.UnmodifiableIterator;
    028
    029/**
    030 * Decorates another {@link Queue} to ensure it can't be altered.
    031 * <p>
    032 * Attempts to modify it will result in an UnsupportedOperationException.
    033 *
    034 * @param <E> the type of elements held in this queue
    035 * @since 4.0
    036 */
    037public final class UnmodifiableQueue<E>
    038        extends AbstractQueueDecorator<E>
    039        implements Unmodifiable {
    040
    041    /** Serialization version */
    042    private static final long serialVersionUID = 1832948656215393357L;
    043
    044    /**
    045     * Factory method to create an unmodifiable queue.
    046     * <p>
    047     * If the queue passed in is already unmodifiable, it is returned.
    048     *
    049     * @param <E> the type of the elements in the queue
    050     * @param queue  the queue to decorate, must not be null
    051     * @return an unmodifiable Queue
    052     * @throws NullPointerException if queue is null
    053     */
    054    public static <E> Queue<E> unmodifiableQueue(final Queue<? extends E> queue) {
    055        if (queue instanceof Unmodifiable) {
    056            @SuppressWarnings("unchecked") // safe to upcast
    057            final Queue<E> tmpQueue = (Queue<E>) queue;
    058            return tmpQueue;
    059        }
    060        return new UnmodifiableQueue<>(queue);
    061    }
    062
    063    //-----------------------------------------------------------------------
    064    /**
    065     * Constructor that wraps (not copies).
    066     *
    067     * @param queue  the queue to decorate, must not be null
    068     * @throws NullPointerException if queue is null
    069     */
    070    @SuppressWarnings("unchecked") // safe to upcast
    071    private UnmodifiableQueue(final Queue<? extends E> queue) {
    072        super((Queue<E>) queue);
    073    }
    074
    075    //-----------------------------------------------------------------------
    076    /**
    077     * Write the collection out using a custom routine.
    078     *
    079     * @param out  the output stream
    080     * @throws IOException if an I/O error occurs while writing to the output stream
    081     */
    082    private void writeObject(final ObjectOutputStream out) throws IOException {
    083        out.defaultWriteObject();
    084        out.writeObject(decorated());
    085    }
    086
    087    /**
    088     * Read the collection in using a custom routine.
    089     *
    090     * @param in  the input stream
    091     * @throws IOException if an I/O error occurs while reading from the input stream
    092     * @throws ClassNotFoundException if the class of a serialized object can not be found
    093     */
    094    @SuppressWarnings("unchecked")
    095    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
    096        in.defaultReadObject();
    097        setCollection((Collection<E>) in.readObject());
    098    }
    099
    100    //-----------------------------------------------------------------------
    101    @Override
    102    public Iterator<E> iterator() {
    103        return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
    104    }
    105
    106    @Override
    107    public boolean add(final Object object) {
    108        throw new UnsupportedOperationException();
    109    }
    110
    111    @Override
    112    public boolean addAll(final Collection<? extends E> coll) {
    113        throw new UnsupportedOperationException();
    114    }
    115
    116    @Override
    117    public void clear() {
    118        throw new UnsupportedOperationException();
    119    }
    120
    121    @Override
    122    public boolean remove(final Object object) {
    123        throw new UnsupportedOperationException();
    124    }
    125
    126    @Override
    127    public boolean removeAll(final Collection<?> coll) {
    128        throw new UnsupportedOperationException();
    129    }
    130
    131    @Override
    132    public boolean retainAll(final Collection<?> coll) {
    133        throw new UnsupportedOperationException();
    134    }
    135
    136    //-----------------------------------------------------------------------
    137
    138    @Override
    139    public boolean offer(final E obj) {
    140        throw new UnsupportedOperationException();
    141    }
    142
    143    @Override
    144    public E poll() {
    145        throw new UnsupportedOperationException();
    146    }
    147
    148    @Override
    149    public E remove() {
    150        throw new UnsupportedOperationException();
    151    }
    152
    153}