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 {}