1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.collections4; 18 19 /** 20 * Defines a functor interface implemented by classes that transform one 21 * object into another. 22 * <p> 23 * A {@code Transformer} converts the input object to the output object. 24 * The input object should be left unchanged. 25 * Transformers are typically used for type conversions, or extracting data 26 * from an object. 27 * </p> 28 * <p> 29 * Standard implementations of common transformers are provided by 30 * {@link TransformerUtils}. These include method invocation, returning a constant, 31 * cloning and returning the string value. 32 * </p> 33 * 34 * @param <I> the input type to the transformer 35 * @param <O> the output type from the transformer 36 * 37 * @since 1.0 38 */ 39 @FunctionalInterface 40 public interface Transformer<I, O> { 41 42 /** 43 * Transforms the input object (leaving it unchanged) into some output object. 44 * 45 * @param input the object to be transformed, should be left unchanged 46 * @return a transformed object 47 * @throws ClassCastException (runtime) if the input is the wrong class 48 * @throws IllegalArgumentException (runtime) if the input is invalid 49 * @throws FunctorException (runtime) if the transform cannot be completed 50 */ 51 O transform(I input); 52 53 }