001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  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,
013     * software distributed under the License is distributed on an
014     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     * KIND, either express or implied.  See the License for the
016     * specific language governing permissions and limitations
017     * under the License.    
018     */ 
019    
020    package org.apache.commons.pipeline.util;
021    
022    /**
023     * An implementation of this interface should define a strategy that will
024     * allow a unique identifier to be generated for an object. This identifier
025     * may be mutually comparable with identifiers generated for a different 
026     * object type; it is used to permit signalling between drivers in
027     * separate pipeline branches.
028     *
029     *
030     */
031    public interface KeyFactory<T,K> {
032        /**
033         * Generates a unique identifier of type K for an object of type T.
034         * @return the newly created identifier
035         */ 
036        public K generateKey(T source);
037        
038        /**
039         * Trivial key factory that produces the object's hash code as a key.
040         */
041        public static class HashKeyFactory implements KeyFactory<Object,Integer> {
042            public Integer generateKey(Object source) {
043                return source.hashCode();
044            }        
045        }
046    }