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
019import java.util.function.Function;
020
021/**
022 * Defines a functor interface implemented by classes that transform one
023 * object into another.
024 * <p>
025 * A {@code Transformer} converts the input object to the output object.
026 * The input object should be left unchanged.
027 * Transformers are typically used for type conversions, or extracting data
028 * from an object.
029 * </p>
030 * <p>
031 * Standard implementations of common transformers are provided by
032 * {@link TransformerUtils}. These include method invocation, returning a constant,
033 * cloning and returning the string value.
034 * </p>
035 *
036 * @param <T> the input type to the transformer
037 * @param <R> the output type from the transformer
038 *
039 * @since 1.0
040 * @deprecated Use {@link Function}.
041 */
042@Deprecated
043public interface Transformer<T, R> extends Function<T, R> {
044
045    @Override
046    default R apply(final T t) {
047        return transform(t);
048    }
049
050    /**
051     * Transforms the input object (leaving it unchanged) into some output object.
052     *
053     * @param input  the object to be transformed, should be left unchanged
054     * @return a transformed object
055     * @throws ClassCastException (runtime) if the input is the wrong class
056     * @throws IllegalArgumentException (runtime) if the input is invalid
057     * @throws FunctorException (runtime) if the transform cannot be completed
058     */
059    R transform(T input);
060
061}