    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.util.Queue;
    020
    021import org.apache.commons.collections4.Transformer;
    022import org.apache.commons.collections4.collection.TransformedCollection;
    023
    024/**
    025 * Decorates another {@link Queue} to transform objects that are added.
    026 * <p>
    027 * The add/offer methods are affected by this class.
    028 * Thus objects must be removed or searched for using their transformed form.
    029 * For example, if the transformation converts Strings to Integers, you must
    030 * use the Integer form to remove objects.
    031 *
    032 * @param <E> the type of elements held in this queue
    033 * @since 4.0
    034 */
    035public class TransformedQueue<E> extends TransformedCollection<E> implements Queue<E> {
    036
    037    /** Serialization version */
    038    private static final long serialVersionUID = -7901091318986132033L;
    039
    040    /**
    041     * Factory method to create a transforming queue.
    042     * <p>
    043     * If there are any elements already in the queue being decorated, they
    044     * are NOT transformed.
    045     * Contrast this with {@link #transformedQueue(Queue, Transformer)}.
    046     *
    047     * @param <E> the type of the elements in the queue
    048     * @param queue  the queue to decorate, must not be null
    049     * @param transformer  the transformer to use for conversion, must not be null
    050     * @return a new transformed Queue
    051     * @throws NullPointerException if queue or transformer is null
    052     */
    053    public static <E> TransformedQueue<E> transformingQueue(final Queue<E> queue,
    054                                                            final Transformer<? super E, ? extends E> transformer) {
    055        return new TransformedQueue<>(queue, transformer);
    056    }
    057
    058    /**
    059     * Factory method to create a transforming queue that will transform
    060     * existing contents of the specified queue.
    061     * <p>
    062     * If there are any elements already in the queue being decorated, they
    063     * will be transformed by this method.
    064     * Contrast this with {@link #transformingQueue(Queue, Transformer)}.
    065     *
    066     * @param <E> the type of the elements in the queue
    067     * @param queue  the queue to decorate, must not be null
    068     * @param transformer  the transformer to use for conversion, must not be null
    069     * @return a new transformed Queue
    070     * @throws NullPointerException if queue or transformer is null
    071     * @since 4.0
    072     */
    073    public static <E> TransformedQueue<E> transformedQueue(final Queue<E> queue,
    074                                                           final Transformer<? super E, ? extends E> transformer) {
    075        // throws IAE if queue or transformer is null
    076        final TransformedQueue<E> decorated = new TransformedQueue<>(queue, transformer);
    077        if (queue.size() > 0) {
    078            @SuppressWarnings("unchecked") // queue is type <E>
    079            final E[] values = (E[]) queue.toArray(); // NOPMD - false positive for generics
    080            queue.clear();
    081            for (final E value : values) {
    082                decorated.decorated().add(transformer.transform(value));
    083            }
    084        }
    085        return decorated;
    086    }
    087
    088    //-----------------------------------------------------------------------
    089    /**
    090     * Constructor that wraps (not copies).
    091     * <p>
    092     * If there are any elements already in the queue being decorated, they
    093     * are NOT transformed.
    094     *
    095     * @param queue  the queue to decorate, must not be null
    096     * @param transformer  the transformer to use for conversion, must not be null
    097     * @throws NullPointerException if queue or transformer is null
    098     */
    099    protected TransformedQueue(final Queue<E> queue, final Transformer<? super E, ? extends E> transformer) {
    100        super(queue, transformer);
    101    }
    102
    103    /**
    104     * Gets the decorated queue.
    105     *
    106     * @return the decorated queue
    107     */
    108    protected Queue<E> getQueue() {
    109        return (Queue<E>) decorated();
    110    }
    111
    112    //-----------------------------------------------------------------------
    113
    114    @Override
    115    public boolean offer(final E obj) {
    116        return getQueue().offer(transform(obj));
    117    }
    118
    119    @Override
    120    public E poll() {
    121        return getQueue().poll();
    122    }
    123
    124    @Override
    125    public E peek() {
    126        return getQueue().peek();
    127    }
    128
    129    @Override
    130    public E element() {
    131        return getQueue().element();
    132    }
    133
    134    @Override
    135    public E remove() {
    136        return getQueue().remove();
    137    }
    138
    139}