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.configuration2.event;
018
019/**
020 * <p>
021 * A data class holding information about an event listener registration.
022 * </p>
023 * <p>
024 * An instance of this class stores all information required to determine
025 * whether a specific event listener is to be invoked for a given event. The
026 * class is used internally by {@link EventListenerList}, but is also useful in
027 * general when information about event listeners is to be stored.
028 * </p>
029 * <p>
030 * Implementation note: Instances of this class are immutable and can safely be
031 * shared between multiple threads or components.
032 * </p>
033 *
034 * @version $Id: EventListenerRegistrationData.java 1842194 2018-09-27 22:24:23Z ggregory $
035 * @since 2.0
036 * @param <T> the type of events processed by the listener
037 */
038public final class EventListenerRegistrationData<T extends Event>
039{
040    /** Constant for the factor used by the calculation of the hash code. */
041    private static final int HASH_FACTOR = 31;
042
043    /** The event type. */
044    private final EventType<T> eventType;
045
046    /** The event listener. */
047    private final EventListener<? super T> listener;
048
049    /**
050     * Creates a new instance of {@code EventListenerRegistrationData}.
051     *
052     * @param type the event type (must not be <b>null</b>)
053     * @param lstnr the event listener (must not be <b>null</b>)
054     * @throws IllegalArgumentException if a required parameter is <b>null</b>
055     */
056    public EventListenerRegistrationData(final EventType<T> type,
057            final EventListener<? super T> lstnr)
058    {
059        if (type == null)
060        {
061            throw new IllegalArgumentException("Event type must not be null!");
062        }
063        if (lstnr == null)
064        {
065            throw new IllegalArgumentException(
066                    "Listener to be registered must not be null!");
067        }
068
069        eventType = type;
070        listener = lstnr;
071    }
072
073    /**
074     * Returns the event type for this listener registration.
075     *
076     * @return the event type
077     */
078    public EventType<T> getEventType()
079    {
080        return eventType;
081    }
082
083    /**
084     * Returns the listener this registration is about.
085     *
086     * @return the event listener
087     */
088    public EventListener<? super T> getListener()
089    {
090        return listener;
091    }
092
093    @Override
094    public int hashCode()
095    {
096        int result = eventType.hashCode();
097        result = HASH_FACTOR * result + listener.hashCode();
098        return result;
099    }
100
101    /**
102     * Compares this object with another one. Two instances of
103     * {@code EventListenerRegistrationData} are considered equal if they
104     * reference the same listener and event type.
105     *
106     * @param obj the object to be compared to
107     * @return a flag whether these objects are equal
108     */
109    @Override
110    public boolean equals(final Object obj)
111    {
112        if (this == obj)
113        {
114            return true;
115        }
116        if (!(obj instanceof EventListenerRegistrationData))
117        {
118            return false;
119        }
120
121        final EventListenerRegistrationData<?> c =
122                (EventListenerRegistrationData<?>) obj;
123        return getListener() == c.getListener()
124                && getEventType().equals(c.getEventType());
125    }
126}