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 * @since 2.0
035 * @param <T> the type of events processed by the listener
036 */
037public final class EventListenerRegistrationData<T extends Event>
038{
039    /** Constant for the factor used by the calculation of the hash code. */
040    private static final int HASH_FACTOR = 31;
041
042    /** The event type. */
043    private final EventType<T> eventType;
044
045    /** The event listener. */
046    private final EventListener<? super T> listener;
047
048    /**
049     * Creates a new instance of {@code EventListenerRegistrationData}.
050     *
051     * @param type the event type (must not be <b>null</b>)
052     * @param lstnr the event listener (must not be <b>null</b>)
053     * @throws IllegalArgumentException if a required parameter is <b>null</b>
054     */
055    public EventListenerRegistrationData(final EventType<T> type,
056            final EventListener<? super T> lstnr)
057    {
058        if (type == null)
059        {
060            throw new IllegalArgumentException("Event type must not be null!");
061        }
062        if (lstnr == null)
063        {
064            throw new IllegalArgumentException(
065                    "Listener to be registered must not be null!");
066        }
067
068        eventType = type;
069        listener = lstnr;
070    }
071
072    /**
073     * Returns the event type for this listener registration.
074     *
075     * @return the event type
076     */
077    public EventType<T> getEventType()
078    {
079        return eventType;
080    }
081
082    /**
083     * Returns the listener this registration is about.
084     *
085     * @return the event listener
086     */
087    public EventListener<? super T> getListener()
088    {
089        return listener;
090    }
091
092    @Override
093    public int hashCode()
094    {
095        int result = eventType.hashCode();
096        result = HASH_FACTOR * result + listener.hashCode();
097        return result;
098    }
099
100    /**
101     * Compares this object with another one. Two instances of
102     * {@code EventListenerRegistrationData} are considered equal if they
103     * reference the same listener and event type.
104     *
105     * @param obj the object to be compared to
106     * @return a flag whether these objects are equal
107     */
108    @Override
109    public boolean equals(final Object obj)
110    {
111        if (this == obj)
112        {
113            return true;
114        }
115        if (!(obj instanceof EventListenerRegistrationData))
116        {
117            return false;
118        }
119
120        final EventListenerRegistrationData<?> c =
121                (EventListenerRegistrationData<?>) obj;
122        return getListener() == c.getListener()
123                && getEventType().equals(c.getEventType());
124    }
125}