001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.functor.example.map;
018    
019    import java.util.Map;
020    
021    import org.apache.commons.functor.BinaryFunction;
022    import org.apache.commons.functor.UnaryFunction;
023    
024    /**
025     * @version $Revision: 666157 $ $Date: 2008-06-10 17:34:23 +0200 (Tue, 10 Jun 2008) $
026     * @author Rodney Waldhoff
027     */
028    @SuppressWarnings("unchecked")
029    public class LazyMap extends FunctoredMap {
030        public LazyMap(Map map, final UnaryFunction factory) {
031            super(map);
032            setOnGet(new BinaryFunction() {
033                public Object evaluate(Object m, Object key) {
034                    Map map = (Map) m;
035                    if (map.containsKey(key)) {
036                        return map.get(key);
037                    } else {
038                        Object value = factory.evaluate(key);
039                        map.put(key,value);
040                        return value;
041                    }
042                }
043            });
044        }
045    }