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 */
017package org.apache.commons.collections4;
018
019/**
020 * Defines a functor interface implemented by classes that transform one
021 * object into another.
022 * <p>
023 * A <code>Transformer</code> converts the input object to the output object.
024 * The input object should be left unchanged.
025 * Transformers are typically used for type conversions, or extracting data
026 * from an object.
027 * </p>
028 * <p>
029 * Standard implementations of common transformers are provided by
030 * {@link TransformerUtils}. These include method invocation, returning a constant,
031 * cloning and returning the string value.
032 * </p>
033 *
034 * @param <I> the input type to the transformer
035 * @param <O> the output type from the transformer
036 *
037 * @since 1.0
038 */
039@FunctionalInterface
040public interface Transformer<I, O> {
041
042    /**
043     * Transforms the input object (leaving it unchanged) into some output object.
044     *
045     * @param input  the object to be transformed, should be left unchanged
046     * @return a transformed object
047     * @throws ClassCastException (runtime) if the input is the wrong class
048     * @throws IllegalArgumentException (runtime) if the input is invalid
049     * @throws FunctorException (runtime) if the transform cannot be completed
050     */
051    O transform(I input);
052
053}