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 * https://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
18 package org.apache.commons.collections4;
19
20 import java.util.function.Function;
21
22 /**
23 * Defines a functor interface implemented by classes that transform one object into another.
24 * <p>
25 * A {@code Transformer} converts the input object to the output object. The input object SHOULD be left unchanged. Transformers are typically used for type
26 * conversions, or extracting data from an object.
27 * </p>
28 * <p>
29 * Standard implementations of common transformers are provided by {@link TransformerUtils}. These include method invocation, returning a constant, cloning and
30 * returning the string value.
31 * </p>
32 *
33 * @param <T> The type of the input to the function.
34 * @param <R> The type of the result of the function.
35 * @since 1.0 This will be deprecated in 5.0 in favor of {@link Function}.
36 */
37 //@Deprecated
38 @FunctionalInterface
39 public interface Transformer<T, R> extends Function<T, R> {
40
41 @Override
42 default R apply(final T t) {
43 return transform(t);
44 }
45
46 /**
47 * Transforms the input object into some output object.
48 * <p>
49 * The input object SHOULD be left unchanged.
50 * </p>
51 *
52 * @param input The object to be transformed, should be left unchanged.
53 * @return A transformed object.
54 * @throws ClassCastException (runtime) if the input is the wrong class.
55 * @throws IllegalArgumentException (runtime) if the input is invalid.
56 * @throws FunctorException (runtime) if the transform cannot be completed.
57 */
58 R transform(T input);
59 }