    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} 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}