1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.collections4.queue;
18
19 import java.util.Queue;
20
21 import org.apache.commons.collections4.Predicate;
22 import org.apache.commons.collections4.collection.PredicatedCollection;
23
24 /**
25 * Decorates another {@link Queue} to validate that additions
26 * match a specified predicate.
27 * <p>
28 * This queue exists to provide validation for the decorated queue.
29 * It is normally created to decorate an empty queue.
30 * If an object cannot be added to the queue, an IllegalArgumentException is thrown.
31 * </p>
32 * <p>
33 * One usage would be to ensure that no null entries are added to the queue.
34 * </p>
35 * <pre>Queue queue = PredicatedQueue.predicatedQueue(new UnboundedFifoQueue(), NotNullPredicate.INSTANCE);</pre>
36 *
37 * @param <E> the type of elements held in this queue
38 * @since 4.0
39 */
40 public class PredicatedQueue<E> extends PredicatedCollection<E> implements Queue<E> {
41
42 /** Serialization version */
43 private static final long serialVersionUID = 2307609000539943581L;
44
45 /**
46 * Factory method to create a predicated (validating) queue.
47 * <p>
48 * If there are any elements already in the queue being decorated, they
49 * are validated.
50 *
51 * @param <E> the type of the elements in the queue
52 * @param Queue the queue to decorate, must not be null
53 * @param predicate the predicate to use for validation, must not be null
54 * @return a new predicated queue
55 * @throws NullPointerException if queue or predicate is null
56 * @throws IllegalArgumentException if the queue contains invalid elements
57 */
58 public static <E> PredicatedQueue<E> predicatedQueue(final Queue<E> Queue,
59 final Predicate<? super E> predicate) {
60 return new PredicatedQueue<>(Queue, predicate);
61 }
62
63 /**
64 * Constructor that wraps (not copies).
65 * <p>
66 * If there are any elements already in the collection being decorated, they
67 * are validated.
68 *
69 * @param queue the queue to decorate, must not be null
70 * @param predicate the predicate to use for validation, must not be null
71 * @throws NullPointerException if queue or predicate is null
72 * @throws IllegalArgumentException if the Queue contains invalid elements
73 */
74 protected PredicatedQueue(final Queue<E> queue, final Predicate<? super E> predicate) {
75 super(queue, predicate);
76 }
77
78 /**
79 * Gets the queue being decorated.
80 *
81 * @return the decorated queue
82 */
83 @Override
84 protected Queue<E> decorated() {
85 return (Queue<E>) super.decorated();
86 }
87
88 @Override
89 public E element() {
90 return decorated().element();
91 }
92
93 /**
94 * Override to validate the object being added to ensure it matches
95 * the predicate.
96 *
97 * @param object the object being added
98 * @return the result of adding to the underlying queue
99 * @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 }