1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.configuration2.event;
18
19 /**
20 * <p>
21 * An interface for configuration implementations which support registration of event listeners.
22 * </p>
23 * <p>
24 * Through the methods provided by this interface it is possible to register and remove listeners for different events
25 * supported by this library. The event type to be handled by a listener must be provided; the specified event listener
26 * must be compatible with this event type. By using generic type parameters, the compiler can check this.
27 * </p>
28 *
29 * @since 2.0
30 */
31 public interface EventSource {
32 /**
33 * Adds an event listener for the specified event type. This listener is notified about events of this type and all its
34 * sub types.
35 *
36 * @param eventType the event type (must not be <b>null</b>)
37 * @param listener the listener to be registered (must not be <b>null</b>)
38 * @param <T> the type of events processed by this listener
39 * @throws IllegalArgumentException if a required parameter is <b>null</b>
40 */
41 <T extends Event> void addEventListener(EventType<T> eventType, EventListener<? super T> listener);
42
43 /**
44 * Removes the event listener registration for the given event type and listener. An event listener instance may be
45 * registered multiple times for different event types. Therefore, when removing a listener the event type of the
46 * registration in question has to be specified. The return value indicates whether a registration was removed. A value
47 * of <b>false</b> means that no such combination of event type and listener was found.
48 *
49 * @param eventType the event type
50 * @param listener the event listener to be removed
51 * @param <T> the type of events processed by this listener
52 * @return a flag whether a listener registration was removed
53 */
54 <T extends Event> boolean removeEventListener(EventType<T> eventType, EventListener<? super T> listener);
55 }