    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 *      https://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
    018package org.apache.commons.collections4;
    019
    020import java.util.function.Function;
    021
    022/**
    023 * Defines a functor interface implemented by classes that transform one object into another.
    024 * <p>
    025 * A {@code Transformer} converts the input object to the output object. The input object SHOULD be left unchanged. Transformers are typically used for type
    026 * conversions, or extracting data from an object.
    027 * </p>
    028 * <p>
    029 * Standard implementations of common transformers are provided by {@link TransformerUtils}. These include method invocation, returning a constant, cloning and
    030 * returning the string value.
    031 * </p>
    032 *
    033 * @param <T> The type of the input to the function.
    034 * @param <R> The type of the result of the function.
    035 * @since 1.0 This will be deprecated in 5.0 in favor of {@link Function}.
    036 */
    037//@Deprecated
    038@FunctionalInterface
    039public interface Transformer<T, R> extends Function<T, R> {
    040
    041    @Override
    042    default R apply(final T t) {
    043        return transform(t);
    044    }
    045
    046    /**
    047     * Transforms the input object into some output object.
    048     * <p>
    049     * The input object SHOULD be left unchanged.
    050     * </p>
    051     *
    052     * @param input The object to be transformed, should be left unchanged.
    053     * @return A transformed object.
    054     * @throws ClassCastException       (runtime) if the input is the wrong class.
    055     * @throws IllegalArgumentException (runtime) if the input is invalid.
    056     * @throws FunctorException         (runtime) if the transform cannot be completed.
    057     */
    058    R transform(T input);
    059}