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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.commons.collections4.queue;

import java.util.Queue;

import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.collection.TransformedCollection;

/**
 * Decorates another {@link Queue} to transform objects that are added.
 * 

* The add/offer methods are affected by this class. * Thus objects must be removed or searched for using their transformed form. * For example, if the transformation converts Strings to Integers, you must * use the Integer form to remove objects. *

* * @param the type of elements held in this queue * @since 4.0 */ public class TransformedQueue extends TransformedCollection implements Queue { /** Serialization version */ private static final long serialVersionUID = -7901091318986132033L; /** * Factory method to create a transforming queue. *

* If there are any elements already in the queue being decorated, they * are NOT transformed. * Contrast this with {@link #transformedQueue(Queue, Transformer)}. * * @param the type of the elements in the queue * @param queue the queue to decorate, must not be null * @param transformer the transformer to use for conversion, must not be null * @return a new transformed Queue * @throws NullPointerException if queue or transformer is null */ public static TransformedQueue transformingQueue(final Queue queue, final Transformer transformer) { return new TransformedQueue<>(queue, transformer); } /** * Factory method to create a transforming queue that will transform * existing contents of the specified queue. *

* If there are any elements already in the queue being decorated, they * will be transformed by this method. * Contrast this with {@link #transformingQueue(Queue, Transformer)}. * * @param the type of the elements in the queue * @param queue the queue to decorate, must not be null * @param transformer the transformer to use for conversion, must not be null * @return a new transformed Queue * @throws NullPointerException if queue or transformer is null * @since 4.0 */ public static TransformedQueue transformedQueue(final Queue queue, final Transformer transformer) { // throws IAE if queue or transformer is null final TransformedQueue decorated = new TransformedQueue<>(queue, transformer); if (queue.size() > 0) { @SuppressWarnings("unchecked") // queue is type final E[] values = (E[]) queue.toArray(); // NOPMD - false positive for generics queue.clear(); for (final E value : values) { decorated.decorated().add(transformer.transform(value)); } } return decorated; } //----------------------------------------------------------------------- /** * Constructor that wraps (not copies). *

* If there are any elements already in the queue being decorated, they * are NOT transformed. * * @param queue the queue to decorate, must not be null * @param transformer the transformer to use for conversion, must not be null * @throws NullPointerException if queue or transformer is null */ protected TransformedQueue(final Queue queue, final Transformer transformer) { super(queue, transformer); } /** * Gets the decorated queue. * * @return the decorated queue */ protected Queue getQueue() { return (Queue) decorated(); } //----------------------------------------------------------------------- @Override public boolean offer(final E obj) { return getQueue().offer(transform(obj)); } @Override public E poll() { return getQueue().poll(); } @Override public E peek() { return getQueue().peek(); } @Override public E element() { return getQueue().element(); } @Override public E remove() { return getQueue().remove(); } }





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