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.collections.functors;
018
019 import java.io.Serializable;
020
021 import org.apache.commons.collections.Transformer;
022
023 /**
024 * Transformer implementation that returns the same constant each time.
025 * <p>
026 * No check is made that the object is immutable. In general, only immutable
027 * objects should use the constant factory. Mutable objects should
028 * use the prototype factory.
029 *
030 * @since Commons Collections 3.0
031 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
032 *
033 * @author Stephen Colebourne
034 */
035 public class ConstantTransformer implements Transformer, Serializable {
036
037 /** Serial version UID */
038 private static final long serialVersionUID = 6374440726369055124L;
039
040 /** Returns null each time */
041 public static final Transformer NULL_INSTANCE = new ConstantTransformer(null);
042
043 /** The closures to call in turn */
044 private final Object iConstant;
045
046 /**
047 * Transformer method that performs validation.
048 *
049 * @param constantToReturn the constant object to return each time in the factory
050 * @return the <code>constant</code> factory.
051 */
052 public static Transformer getInstance(Object constantToReturn) {
053 if (constantToReturn == null) {
054 return NULL_INSTANCE;
055 }
056 return new ConstantTransformer(constantToReturn);
057 }
058
059 /**
060 * Constructor that performs no validation.
061 * Use <code>getInstance</code> if you want that.
062 *
063 * @param constantToReturn the constant to return each time
064 */
065 public ConstantTransformer(Object constantToReturn) {
066 super();
067 iConstant = constantToReturn;
068 }
069
070 /**
071 * Transforms the input by ignoring it and returning the stored constant instead.
072 *
073 * @param input the input object which is ignored
074 * @return the stored constant
075 */
076 public Object transform(Object input) {
077 return iConstant;
078 }
079
080 /**
081 * Gets the constant.
082 *
083 * @return the constant
084 * @since Commons Collections 3.1
085 */
086 public Object getConstant() {
087 return iConstant;
088 }
089
090 }