/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.configuration2.event;

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