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 that will transform
043     * existing contents of the specified queue.
044     * <p>
045     * If there are any elements already in the queue being decorated, they
046     * will be transformed by this method.
047     * Contrast this with {@link #transformingQueue(Queue, Transformer)}.
048     *
049     * @param <E> the type of the elements in the queue
050     * @param queue  the queue to decorate, must not be null
051     * @param transformer  the transformer to use for conversion, must not be null
052     * @return a new transformed Queue
053     * @throws NullPointerException if queue or transformer is null
054     * @since 4.0
055     */
056    public static <E> TransformedQueue<E> transformedQueue(final Queue<E> queue,
057                                                           final Transformer<? super E, ? extends E> transformer) {
058        // throws IAE if queue or transformer is null
059        final TransformedQueue<E> decorated = new TransformedQueue<>(queue, transformer);
060        if (!queue.isEmpty()) {
061            @SuppressWarnings("unchecked") // queue is type <E>
062            final E[] values = (E[]) queue.toArray(); // NOPMD - false positive for generics
063            queue.clear();
064            for (final E value : values) {
065                decorated.decorated().add(transformer.apply(value));
066            }
067        }
068        return decorated;
069    }
070
071    /**
072     * Factory method to create a transforming queue.
073     * <p>
074     * If there are any elements already in the queue being decorated, they
075     * are NOT transformed.
076     * Contrast this with {@link #transformedQueue(Queue, Transformer)}.
077     *
078     * @param <E> the type of the elements in the queue
079     * @param queue  the queue to decorate, must not be null
080     * @param transformer  the transformer to use for conversion, must not be null
081     * @return a new transformed Queue
082     * @throws NullPointerException if queue or transformer is null
083     */
084    public static <E> TransformedQueue<E> transformingQueue(final Queue<E> queue,
085                                                            final Transformer<? super E, ? extends E> transformer) {
086        return new TransformedQueue<>(queue, transformer);
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    @Override
104    public E element() {
105        return getQueue().element();
106    }
107
108    /**
109     * Gets the decorated queue.
110     *
111     * @return the decorated queue
112     */
113    protected Queue<E> getQueue() {
114        return (Queue<E>) decorated();
115    }
116
117    @Override
118    public boolean offer(final E obj) {
119        return getQueue().offer(transform(obj));
120    }
121
122    @Override
123    public E peek() {
124        return getQueue().peek();
125    }
126
127    @Override
128    public E poll() {
129        return getQueue().poll();
130    }
131
132    @Override
133    public E remove() {
134        return getQueue().remove();
135    }
136
137}