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 * Definition of a generic event listener interface.
022 * </p>
023 * <p>
024 * This event listener interface is used throughout the
025 * <em>Commons Configuration</em> library for reacting on all kinds of supported
026 * events. The interface is pretty minimalistic, defining only a single
027 * {@code onEvent()} method. This simplifies the implementation of custom event
028 * listeners and also supports the new language features introduced with Java 8
029 * ({@code EventListener} is a functional interface and thus can be represented
030 * by a Lambda expression).
031 * </p>
032 *
033 * @since 2.0
034 * @param <T> the type of events this listener can process
035 */
036public interface EventListener<T extends Event>
037{
038    /**
039     * Notifies this event listener about the arrival of a new event. Typically,
040     * event listeners are registered at an event source providing an
041     * {@link EventType}. This event type acts as a filter; all events matched
042     * by the filter are passed to the listener. The type parameters defined by
043     * the {@code EventType} class and this interface guarantee that the events
044     * delivered to the handler are compatible with the concrete method
045     * signature of {@code onEvent()}.
046     *
047     * @param event the event
048     */
049    void onEvent(T event);
050}