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