001    /**
002     * Copyright (c) 2008-2009 Apple Inc. All rights reserved.
003     * Copyright (C) 2012 FuseSource, Inc.
004     * http://fusesource.com
005     *
006     * Licensed under the Apache License, Version 2.0 (the "License");
007     * you may not use this file except in compliance with the License.
008     * You may obtain a copy of the License at
009     *
010     *    http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    
019    package org.fusesource.hawtdispatch;
020    
021    /**
022     * <p>
023     * The EventAggregator interface is used by the {@link CustomDispatchSource} objects to handle
024     * coalescing data before passing it to the application.  Implementations of this class should
025     * be stateless to remain thread-safe.  You can also use one of several built in implementations:
026     * </p>
027     *
028     * <ul>
029     * <li>{@link EventAggregators#INTEGER_ADD}</li>
030     * <li>{@link EventAggregators#INTEGER_OR}</li>
031     * <li>{@link EventAggregators#LONG_ADD}</li>
032     * <li>{@link EventAggregators#LONG_OR}</li> 
033     * </ul>
034     *
035     * @author <a href="http://hiramchirino.com">Hiram Chirino</a>
036     */
037    public interface EventAggregator<Event, MergedEvent> {
038    
039        /**
040         * <p>
041         * Merge the given event with the previous event values.
042         * </p>
043         *
044         * @param previous may be null
045         * @param event the value that should be merged
046         * @return a newly merged result
047         */
048        public MergedEvent mergeEvent(MergedEvent previous, Event event);
049    
050        /**
051         * <p>
052         * Merge the given events with the previous event values.
053         * </p>
054         *
055         * @param previous the value of previous merges
056         * @param events the value of more merges
057         * @return a newly merged result
058         */
059        public MergedEvent mergeEvents(MergedEvent previous, MergedEvent events);
060    
061    }