1 //
2 // ========================================================================
3 // Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
4 // ------------------------------------------------------------------------
5 // All rights reserved. This program and the accompanying materials
6 // are made available under the terms of the Eclipse Public License v1.0
7 // and Apache License v2.0 which accompanies this distribution.
8 //
9 // The Eclipse Public License is available at
10 // http://www.eclipse.org/legal/epl-v10.html
11 //
12 // The Apache License v2.0 is available at
13 // http://www.opensource.org/licenses/apache2.0.php
14 //
15 // You may elect to redistribute this code under either of these licenses.
16 // ========================================================================
17 //
18
19 package org.eclipse.jetty.util;
20
21 /**
22 * <p>A callback abstraction that handles completed/failed events of asynchronous operations.</p>
23 *
24 * <p>Semantically this is equivalent to an optimise Promise<Void>, but callback is a more meaningful
25 * name than EmptyPromise</p>
26 */
27 public interface Callback
28 {
29 /**
30 * <p>Callback invoked when the operation completes.</p>
31 *
32 * @see #failed(Throwable)
33 */
34 public abstract void succeeded();
35
36 /**
37 * <p>Callback invoked when the operation fails.</p>
38 * @param x the reason for the operation failure
39 */
40 public void failed(Throwable x);
41
42 /**
43 * <p>Empty implementation of {@link Callback}</p>
44 */
45 public static class Adapter implements Callback
46 {
47 /**
48 * Instance of Adapter that can be used when the callback methods need an empty
49 * implementation without incurring in the cost of allocating a new Adapter object.
50 */
51 public static final Adapter INSTANCE = new Adapter();
52
53 @Override
54 public void succeeded()
55 {
56 }
57
58 @Override
59 public void failed(Throwable x)
60 {
61 }
62 }
63 }