1 /**
2 * Copyright 2008 Atlassian Pty Ltd
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.atlassian.util.concurrent;
18
19 import net.jcip.annotations.ThreadSafe;
20
21 /**
22 * A Function that resolves Descriptors (of type D) to a Resource (of type R).
23 * <p>
24 * Semantically, this could be a Factory, Generator, Builder, Closure, Transformer, Resolver or
25 * something else entirely. No particular guarantees are implied by this interface apart from
26 * idempotence (see below). Specifically, implementations may or may not return or accept null and
27 * can optionally block until elements are available or throw {@link RuntimeException runtime
28 * exceptions} if the input is not acceptable for some reason. Any clients that require a firmer
29 * contract should subclass this interface and document their requirements.
30 * <p>
31 * It is expected that for any two calls to {@link #get(Object)} D the returned resource will be
32 * semantically the same, ie. that the call is effectively idempotent. Any implementation that
33 * violates this should document the fact. It is not necessary that the resolved object is the same
34 * instance or even implements {@link #equals(Object)} and {@link #hashCode()} however.
35 * <p>
36 * As this interface requires idempotence implementations should be reentrant and thread-safe.
37 *
38 * @param <D> the descriptor type.
39 * @param <R> the resource type it resolves to.
40 * @author Jed Wesley-Smith
41 */
42 @ThreadSafe public interface Function<D, R> {
43 /**
44 * Resolves an output <R> where an input <D> is given.
45 *
46 * @param input an object of type D.
47 * @return the output of type R.
48 */
49 R get(D input);
50 }