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