rt/emul/compact/src/main/java/java/lang/SafeVarargs.java
author Jaroslav Tulach <jaroslav.tulach@apidesign.org>
Tue, 26 Feb 2013 16:54:16 +0100
changeset 772 d382dacfd73f
parent 559 emul/compact/src/main/java/java/lang/SafeVarargs.java@9ec5ddf175b5
permissions -rw-r--r--
Moving modules around so the runtime is under one master pom and can be built without building other modules that are in the repository
     1 /*
     2  * Copyright (c) 2010, 2011, 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 
    26 package java.lang;
    27 
    28 import 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}.
    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  * @jls 4.7 Reifiable Types
    86  * @jls 8.4.1 Formal Parameters
    87  */
    88 @Documented
    89 @Retention(RetentionPolicy.RUNTIME)
    90 @Target({ElementType.CONSTRUCTOR, ElementType.METHOD})
    91 public @interface SafeVarargs {}