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}