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Commons Collections example source code file (MapTransformer.java)

This example Commons Collections source code file (MapTransformer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

io, map, map, maptransformer, maptransformer, object, object, serializable, transformer, transformer, util

The Commons Collections MapTransformer.java source code

 *  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.collections.functors;

import java.io.Serializable;
import java.util.Map;

import org.apache.commons.collections.Transformer;

 * Transformer implementation that returns the value held in a specified map
 * using the input parameter as a key.
 * @since Commons Collections 3.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 * @author Stephen Colebourne
public final class MapTransformer implements Transformer, Serializable {

    /** Serial version UID */
    private static final long serialVersionUID = 862391807045468939L;
    /** The map of data to lookup in */
    private final Map iMap;

     * Factory to create the transformer.
     * <p>
     * If the map is null, a transformer that always returns null is returned.
     * @param map the map, not cloned
     * @return the transformer
    public static Transformer getInstance(Map map) {
        if (map == null) {
            return ConstantTransformer.NULL_INSTANCE;
        return new MapTransformer(map);

     * Constructor that performs no validation.
     * Use <code>getInstance if you want that.
     * @param map  the map to use for lookup, not cloned
    private MapTransformer(Map map) {
        iMap = map;

     * Transforms the input to result by looking it up in a <code>Map.
     * @param input  the input object to transform
     * @return the transformed result
    public Object transform(Object input) {
        return iMap.get(input);

     * Gets the map to lookup in.
     * @return the map
     * @since Commons Collections 3.1
    public Map getMap() {
        return iMap;


Other Commons Collections examples (source code examples)

Here is a short list of links related to this Commons Collections MapTransformer.java source code file:

my book on functional programming


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