1/*
2 * Copyright (c) 2010, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26package java.lang;
27
28import java.lang.annotation.*;
29
30/**
31 * A programmer assertion that the body of the annotated method or
32 * constructor does not perform potentially unsafe operations on its
33 * varargs parameter.  Applying this annotation to a method or
34 * constructor suppresses unchecked warnings about a
35 * <i>non-reifiable</i> variable arity (vararg) type and suppresses
36 * unchecked warnings about parameterized array creation at call
37 * sites.
38 *
39 * <p> In addition to the usage restrictions imposed by its {@link
40 * Target @Target} meta-annotation, compilers are required to implement
41 * additional usage restrictions on this annotation type; it is a
42 * compile-time error if a method or constructor declaration is
43 * annotated with a {@code @SafeVarargs} annotation, and either:
44 * <ul>
45 * <li>  the declaration is a fixed arity method or constructor
46 *
47 * <li> the declaration is a variable arity method that is neither
48 * {@code static} nor {@code final} nor {@code private}.
49 *
50 * </ul>
51 *
52 * <p> Compilers are encouraged to issue warnings when this annotation
53 * type is applied to a method or constructor declaration where:
54 *
55 * <ul>
56 *
57 * <li> The variable arity parameter has a reifiable element type,
58 * which includes primitive types, {@code Object}, and {@code String}.
59 * (The unchecked warnings this annotation type suppresses already do
60 * not occur for a reifiable element type.)
61 *
62 * <li> The body of the method or constructor declaration performs
63 * potentially unsafe operations, such as an assignment to an element
64 * of the variable arity parameter's array that generates an unchecked
65 * warning.  Some unsafe operations do not trigger an unchecked
66 * warning.  For example, the aliasing in
67 *
68 * <blockquote><pre>
69 * &#64;SafeVarargs // Not actually safe!
70 * static void m(List&lt;String&gt;... stringLists) {
71 *   Object[] array = stringLists;
72 *   List&lt;Integer&gt; tmpList = Arrays.asList(42);
73 *   array[0] = tmpList; // Semantically invalid, but compiles without warnings
74 *   String s = stringLists[0].get(0); // Oh no, ClassCastException at runtime!
75 * }
76 * </pre></blockquote>
77 *
78 * leads to a {@code ClassCastException} at runtime.
79 *
80 * <p>Future versions of the platform may mandate compiler errors for
81 * such unsafe operations.
82 *
83 * </ul>
84 *
85 * @since 1.7
86 * @jls 4.7 Reifiable Types
87 * @jls 8.4.1 Formal Parameters
88 * @jls 9.6.4.7 @SafeVarargs
89 */
90@Documented
91@Retention(RetentionPolicy.RUNTIME)
92@Target({ElementType.CONSTRUCTOR, ElementType.METHOD})
93public @interface SafeVarargs {}
94