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.configuration2.event;
18
19 /**
20 * <p>
21 * A data class holding information about an event listener registration.
22 * </p>
23 * <p>
24 * An instance of this class stores all information required to determine whether a specific event listener is to be
25 * invoked for a given event. The class is used internally by {@link EventListenerList}, but is also useful in general
26 * when information about event listeners is to be stored.
27 * </p>
28 * <p>
29 * Implementation note: Instances of this class are immutable and can safely be shared between multiple threads or
30 * components.
31 * </p>
32 *
33 * @param <T> the type of events processed by the listener
34 * @since 2.0
35 */
36 public final class EventListenerRegistrationData<T extends Event> {
37 /** Constant for the factor used by the calculation of the hash code. */
38 private static final int HASH_FACTOR = 31;
39
40 /** The event type. */
41 private final EventType<T> eventType;
42
43 /** The event listener. */
44 private final EventListener<? super T> listener;
45
46 /**
47 * Creates a new instance of {@code EventListenerRegistrationData}.
48 *
49 * @param type the event type (must not be <strong>null</strong>)
50 * @param lstnr the event listener (must not be <strong>null</strong>)
51 * @throws IllegalArgumentException if a required parameter is <strong>null</strong>
52 */
53 public EventListenerRegistrationData(final EventType<T> type, final EventListener<? super T> lstnr) {
54 if (type == null) {
55 throw new IllegalArgumentException("Event type must not be null!");
56 }
57 if (lstnr == null) {
58 throw new IllegalArgumentException("Listener to be registered must not be null!");
59 }
60
61 eventType = type;
62 listener = lstnr;
63 }
64
65 /**
66 * Compares this object with another one. Two instances of {@code EventListenerRegistrationData} are considered equal if
67 * they reference the same listener and event type.
68 *
69 * @param obj the object to be compared to
70 * @return a flag whether these objects are equal
71 */
72 @Override
73 public boolean equals(final Object obj) {
74 if (this == obj) {
75 return true;
76 }
77 if (!(obj instanceof EventListenerRegistrationData)) {
78 return false;
79 }
80
81 final EventListenerRegistrationData<?> c = (EventListenerRegistrationData<?>) obj;
82 return getListener() == c.getListener() && getEventType().equals(c.getEventType());
83 }
84
85 /**
86 * Gets the event type for this listener registration.
87 *
88 * @return the event type
89 */
90 public EventType<T> getEventType() {
91 return eventType;
92 }
93
94 /**
95 * Gets the listener this registration is about.
96 *
97 * @return the event listener
98 */
99 public EventListener<? super T> getListener() {
100 return listener;
101 }
102
103 @Override
104 public int hashCode() {
105 final int result = eventType.hashCode();
106 return HASH_FACTOR * result + listener.hashCode();
107 }
108 }