    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 * </p>
    032 *
    033 * @param <E> the type of elements held in this queue
    034 * @since 4.0
    035 */
    036public class TransformedQueue<E> extends TransformedCollection<E> implements Queue<E> {
    037
    038    /** Serialization version */
    039    private static final long serialVersionUID = -7901091318986132033L;
    040
    041    /**
    042     * Factory method to create a transforming queue.
    043     * <p>
    044     * If there are any elements already in the queue being decorated, they
    045     * are NOT transformed.
    046     * Contrast this with {@link #transformedQueue(Queue, Transformer)}.
    047     *
    048     * @param <E> the type of the elements in the queue
    049     * @param queue  the queue to decorate, must not be null
    050     * @param transformer  the transformer to use for conversion, must not be null
    051     * @return a new transformed Queue
    052     * @throws NullPointerException if queue or transformer is null
    053     */
    054    public static <E> TransformedQueue<E> transformingQueue(final Queue<E> queue,
    055                                                            final Transformer<? super E, ? extends E> transformer) {
    056        return new TransformedQueue<>(queue, transformer);
    057    }
    058
    059    /**
    060     * Factory method to create a transforming queue that will transform
    061     * existing contents of the specified queue.
    062     * <p>
    063     * If there are any elements already in the queue being decorated, they
    064     * will be transformed by this method.
    065     * Contrast this with {@link #transformingQueue(Queue, Transformer)}.
    066     *
    067     * @param <E> the type of the elements in the queue
    068     * @param queue  the queue to decorate, must not be null
    069     * @param transformer  the transformer to use for conversion, must not be null
    070     * @return a new transformed Queue
    071     * @throws NullPointerException if queue or transformer is null
    072     * @since 4.0
    073     */
    074    public static <E> TransformedQueue<E> transformedQueue(final Queue<E> queue,
    075                                                           final Transformer<? super E, ? extends E> transformer) {
    076        // throws IAE if queue or transformer is null
    077        final TransformedQueue<E> decorated = new TransformedQueue<>(queue, transformer);
    078        if (queue.size() > 0) {
    079            @SuppressWarnings("unchecked") // queue is type <E>
    080            final E[] values = (E[]) queue.toArray(); // NOPMD - false positive for generics
    081            queue.clear();
    082            for (final E value : values) {
    083                decorated.decorated().add(transformer.transform(value));
    084            }
    085        }
    086        return decorated;
    087    }
    088
    089    //-----------------------------------------------------------------------
    090    /**
    091     * Constructor that wraps (not copies).
    092     * <p>
    093     * If there are any elements already in the queue being decorated, they
    094     * are NOT transformed.
    095     *
    096     * @param queue  the queue to decorate, must not be null
    097     * @param transformer  the transformer to use for conversion, must not be null
    098     * @throws NullPointerException if queue or transformer is null
    099     */
    100    protected TransformedQueue(final Queue<E> queue, final Transformer<? super E, ? extends E> transformer) {
    101        super(queue, transformer);
    102    }
    103
    104    /**
    105     * Gets the decorated queue.
    106     *
    107     * @return the decorated queue
    108     */
    109    protected Queue<E> getQueue() {
    110        return (Queue<E>) decorated();
    111    }
    112
    113    //-----------------------------------------------------------------------
    114
    115    @Override
    116    public boolean offer(final E obj) {
    117        return getQueue().offer(transform(obj));
    118    }
    119
    120    @Override
    121    public E poll() {
    122        return getQueue().poll();
    123    }
    124
    125    @Override
    126    public E peek() {
    127        return getQueue().peek();
    128    }
    129
    130    @Override
    131    public E element() {
    132        return getQueue().element();
    133    }
    134
    135    @Override
    136    public E remove() {
    137        return getQueue().remove();
    138    }
    139
    140}