transformer.java

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/*
 *  Copyright 2001-2004 The Apache Software Foundation
 *
 *  Licensed 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;

/**
 * Defines a functor interface implemented by classes that transform one
 * object into another.
 * <p>
 * A <code>Transformer</code> converts the input object to the output object.
 * The input object should be left unchanged.
 * Transformers are typically used for type conversions, or extracting data
 * from an object.
 * <p>
 * Standard implementations of common transformers are provided by
 * {@link TransformerUtils}. These include method invokation, returning a constant,
 * cloning and returning the string value.
 * 
 * @since Commons Collections 1.0
 * @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
 * 
 * @author James Strachan
 * @author Stephen Colebourne
 */
public interface Transformer {

    /**
     * Transforms the input object (leaving it unchanged) into some output object.
     *
     * @param input  the object to be transformed, should be left unchanged
     * @return a transformed object
     * @throws ClassCastException (runtime) if the input is the wrong class
     * @throws IllegalArgumentException (runtime) if the input is invalid
     * @throws FunctorException (runtime) if the transform cannot be completed
     */
    public Object transform(Object input);

}