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}