1 /*
2 * Copyright (C) 2015, Google Inc.
3 * and other copyright owners as documented in the project's IP log.
4 *
5 * This program and the accompanying materials are made available
6 * under the terms of the Eclipse Distribution License v1.0 which
7 * accompanies this distribution, is reproduced below, and is
8 * available at http://www.eclipse.org/org/documents/edl-v10.php
9 *
10 * All rights reserved.
11 *
12 * Redistribution and use in source and binary forms, with or
13 * without modification, are permitted provided that the following
14 * conditions are met:
15 *
16 * - Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 *
19 * - Redistributions in binary form must reproduce the above
20 * copyright notice, this list of conditions and the following
21 * disclaimer in the documentation and/or other materials provided
22 * with the distribution.
23 *
24 * - Neither the name of the Eclipse Foundation, Inc. nor the
25 * names of its contributors may be used to endorse or promote
26 * products derived from this software without specific prior
27 * written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
30 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
31 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
32 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
33 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
34 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
35 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
36 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
37 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
38 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
41 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
42 */
43
44 package org.eclipse.jgit.annotations;
45
46 import static java.lang.annotation.ElementType.FIELD;
47 import static java.lang.annotation.ElementType.LOCAL_VARIABLE;
48 import static java.lang.annotation.ElementType.METHOD;
49 import static java.lang.annotation.ElementType.PARAMETER;
50
51 import java.lang.annotation.Documented;
52 import java.lang.annotation.Retention;
53 import java.lang.annotation.RetentionPolicy;
54 import java.lang.annotation.Target;
55
56 /**
57 * Marks types that can hold the value {@code null} at run time.
58 * <p>
59 * Unlike {@code org.eclipse.jdt.annotation.Nullable}, this has run-time
60 * retention, allowing the annotation to be recognized by
61 * <a href="https://github.com/google/guice/wiki/UseNullable">Guice</a>. Unlike
62 * {@code javax.annotation.Nullable}, this does not involve importing new classes
63 * to a standard (Java EE) package, so it can be deployed in an OSGi container
64 * without running into
65 * <a href="http://wiki.osgi.org/wiki/Split_Packages">split-package</a>
66 * <a href="https://gerrit-review.googlesource.com/50112">problems</a>.
67 * <p>
68 * You can use this annotation to qualify a type in a method signature or local
69 * variable declaration. The entity whose type has this annotation is allowed to
70 * hold the value {@code null} at run time. This allows annotation based null
71 * analysis to infer that
72 * <ul>
73 * <li>Binding a {@code null} value to the entity is legal.
74 * <li>Dereferencing the entity is unsafe and can trigger a
75 * {@code NullPointerException}.
76 * </ul>
77 * <p>
78 * To avoid a dependency on Java 8, this annotation does not use
79 * {@link Target @Target} {@code TYPE_USE}. That may change when JGit starts
80 * requiring Java 8.
81 * <p>
82 * <b>Warning:</b> Please do not use this annotation on arrays. Different
83 * annotation processors treat {@code @Nullable Object[]} differently: some
84 * treat it as an array of nullable objects, for consistency with versions of
85 * {@code Nullable} defined with {@code @Target} {@code TYPE_USE}, while others
86 * treat it as a nullable array of objects. JGit therefore avoids using this
87 * annotation on arrays altogether.
88 *
89 * @see <a href=
90 * "http://types.cs.washington.edu/checker-framework/current/checker-framework-manual.html#faq-array-syntax-meaning">
91 * The checker-framework manual</a>
92 * @since 4.2
93 */
94 @Documented
95 @Retention(RetentionPolicy.RUNTIME)
96 @Target({ FIELD, METHOD, PARAMETER, LOCAL_VARIABLE })
97 public @interface Nullable {
98 // marker annotation with no members
99 }