    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.Predicate;
    022import org.apache.commons.collections4.collection.PredicatedCollection;
    023
    024/**
    025 * Decorates another {@link Queue} to validate that additions
    026 * match a specified predicate.
    027 * <p>
    028 * This queue exists to provide validation for the decorated queue.
    029 * It is normally created to decorate an empty queue.
    030 * If an object cannot be added to the queue, an IllegalArgumentException is thrown.
    031 * </p>
    032 * <p>
    033 * One usage would be to ensure that no null entries are added to the queue.
    034 * </p>
    035 * <pre>Queue queue = PredicatedQueue.predicatedQueue(new UnboundedFifoQueue(), NotNullPredicate.INSTANCE);</pre>
    036 *
    037 * @param <E> the type of elements held in this queue
    038 * @since 4.0
    039 */
    040public class PredicatedQueue<E> extends PredicatedCollection<E> implements Queue<E> {
    041
    042    /** Serialization version */
    043    private static final long serialVersionUID = 2307609000539943581L;
    044
    045    /**
    046     * Factory method to create a predicated (validating) queue.
    047     * <p>
    048     * If there are any elements already in the queue being decorated, they
    049     * are validated.
    050     *
    051     * @param <E> the type of the elements in the queue
    052     * @param Queue  the queue to decorate, must not be null
    053     * @param predicate  the predicate to use for validation, must not be null
    054     * @return a new predicated queue
    055     * @throws NullPointerException if queue or predicate is null
    056     * @throws IllegalArgumentException if the queue contains invalid elements
    057     */
    058    public static <E> PredicatedQueue<E> predicatedQueue(final Queue<E> Queue,
    059                                                          final Predicate<? super E> predicate) {
    060        return new PredicatedQueue<>(Queue, predicate);
    061    }
    062
    063    /**
    064     * Constructor that wraps (not copies).
    065     * <p>
    066     * If there are any elements already in the collection being decorated, they
    067     * are validated.
    068     *
    069     * @param queue  the queue to decorate, must not be null
    070     * @param predicate  the predicate to use for validation, must not be null
    071     * @throws NullPointerException if queue or predicate is null
    072     * @throws IllegalArgumentException if the Queue contains invalid elements
    073     */
    074    protected PredicatedQueue(final Queue<E> queue, final Predicate<? super E> predicate) {
    075        super(queue, predicate);
    076    }
    077
    078    /**
    079     * Gets the queue being decorated.
    080     *
    081     * @return the decorated queue
    082     */
    083    @Override
    084    protected Queue<E> decorated() {
    085        return (Queue<E>) super.decorated();
    086    }
    087
    088    @Override
    089    public E element() {
    090        return decorated().element();
    091    }
    092
    093    /**
    094     * Override to validate the object being added to ensure it matches
    095     * the predicate.
    096     *
    097     * @param object  the object being added
    098     * @return the result of adding to the underlying queue
    099     * @throws IllegalArgumentException if the add is invalid
    100     */
    101    @Override
    102    public boolean offer(final E object) {
    103        validate(object);
    104        return decorated().offer(object);
    105    }
    106
    107    @Override
    108    public E peek() {
    109        return decorated().peek();
    110    }
    111
    112    @Override
    113    public E poll() {
    114        return decorated().poll();
    115    }
    116
    117    @Override
    118    public E remove() {
    119        return decorated().remove();
    120    }
    121
    122}