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 }