https://commons.apache.org/proper/commons-configuration/: Tools to assist in the reading of configuration/preferences files in various formats (The Apache Software Foundation)
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/*
 * 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;



An interface for configuration implementations which support registration of
event listeners.




Through the methods provided by this interface it is possible to register and
remove listeners for different events supported by this library. The event
type to be handled by a listener must be provided; the specified event listener
must be compatible with this event type. By using generic type parameters, the
compiler can check this.



Since:2.0
/**
 * <p>
 * An interface for configuration implementations which support registration of
 * event listeners.
 * </p>
 * <p>
 * Through the methods provided by this interface it is possible to register and
 * remove listeners for different events supported by this library. The event
 * type to be handled by a listener must be provided; the specified event listener
 * must be compatible with this event type. By using generic type parameters, the
 * compiler can check this.
 * </p>
 *
 * @since 2.0
 */
public interface EventSource
{
    
Adds an event listener for the specified event type. This listener is
notified about events of this type and all its sub types.

Params:
  • eventType – the event type (must not be null)
  • listener – the listener to be registered (must not be null)
Type parameters:
  • <T> – the type of events processed by this listener
Throws:
/**
     * Adds an event listener for the specified event type. This listener is
     * notified about events of this type and all its sub types.
     *
     * @param eventType the event type (must not be <b>null</b>)
     * @param listener the listener to be registered (must not be <b>null</b>)
     * @param <T> the type of events processed by this listener
     * @throws IllegalArgumentException if a required parameter is <b>null</b>
     */
    <T extends Event> void addEventListener(EventType<T> eventType,
            EventListener<? super T> listener);

    
Removes the event listener registration for the given event type and
listener. An event listener instance may be registered multiple times for
different event types. Therefore, when removing a listener the event type
of the registration in question has to be specified. The return value
indicates whether a registration was removed. A value of false
means that no such combination of event type and listener was found.

Params:
  • eventType – the event type
  • listener – the event listener to be removed
Type parameters:
  • <T> – the type of events processed by this listener
Returns:a flag whether a listener registration was removed
/**
     * Removes the event listener registration for the given event type and
     * listener. An event listener instance may be registered multiple times for
     * different event types. Therefore, when removing a listener the event type
     * of the registration in question has to be specified. The return value
     * indicates whether a registration was removed. A value of <b>false</b>
     * means that no such combination of event type and listener was found.
     *
     * @param eventType the event type
     * @param listener the event listener to be removed
     * @param <T> the type of events processed by this listener
     * @return a flag whether a listener registration was removed
     */
    <T extends Event> boolean removeEventListener(EventType<T> eventType,
            EventListener<? super T> listener);
}