1 /*
2 * Copyright (C) 2015, Google Inc. and others
3 *
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Distribution License v. 1.0 which is available at
6 * https://www.eclipse.org/org/documents/edl-v10.php.
7 *
8 * SPDX-License-Identifier: BSD-3-Clause
9 */
10
11 package org.eclipse.jgit.annotations;
12
13 import static java.lang.annotation.ElementType.FIELD;
14 import static java.lang.annotation.ElementType.LOCAL_VARIABLE;
15 import static java.lang.annotation.ElementType.METHOD;
16 import static java.lang.annotation.ElementType.PARAMETER;
17
18 import java.lang.annotation.Documented;
19 import java.lang.annotation.Retention;
20 import java.lang.annotation.RetentionPolicy;
21 import java.lang.annotation.Target;
22
23 /**
24 * Marks types that can hold the value {@code null} at run time.
25 * <p>
26 * Unlike {@code org.eclipse.jdt.annotation.Nullable}, this has run-time
27 * retention, allowing the annotation to be recognized by
28 * <a href="https://github.com/google/guice/wiki/UseNullable">Guice</a>. Unlike
29 * {@code javax.annotation.Nullable}, this does not involve importing new classes
30 * to a standard (Java EE) package, so it can be deployed in an OSGi container
31 * without running into
32 * <a href="http://wiki.osgi.org/wiki/Split_Packages">split-package</a>
33 * <a href="https://gerrit-review.googlesource.com/50112">problems</a>.
34 * <p>
35 * You can use this annotation to qualify a type in a method signature or local
36 * variable declaration. The entity whose type has this annotation is allowed to
37 * hold the value {@code null} at run time. This allows annotation based null
38 * analysis to infer that
39 * <ul>
40 * <li>Binding a {@code null} value to the entity is legal.
41 * <li>Dereferencing the entity is unsafe and can trigger a
42 * {@code NullPointerException}.
43 * </ul>
44 * <p>
45 * To avoid a dependency on Java 8, this annotation does not use
46 * {@link Target @Target} {@code TYPE_USE}. That may change when JGit starts
47 * requiring Java 8.
48 * <p>
49 * <b>Warning:</b> Please do not use this annotation on arrays. Different
50 * annotation processors treat {@code @Nullable Object[]} differently: some
51 * treat it as an array of nullable objects, for consistency with versions of
52 * {@code Nullable} defined with {@code @Target} {@code TYPE_USE}, while others
53 * treat it as a nullable array of objects. JGit therefore avoids using this
54 * annotation on arrays altogether.
55 *
56 * @see <a href=
57 * "http://types.cs.washington.edu/checker-framework/current/checker-framework-manual.html#faq-array-syntax-meaning">
58 * The checker-framework manual</a>
59 * @since 4.2
60 */
61 @Documented
62 @Retention(RetentionPolicy.RUNTIME)
63 @Target({ FIELD, METHOD, PARAMETER, LOCAL_VARIABLE })
64 public @interface Nullable {
65 // marker annotation with no members
66 }