jaroslav@559: /*
jaroslav@559:  * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
jaroslav@559:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@559:  *
jaroslav@559:  * This code is free software; you can redistribute it and/or modify it
jaroslav@559:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@559:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@559:  * particular file as subject to the "Classpath" exception as provided
jaroslav@559:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@559:  *
jaroslav@559:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@559:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@559:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@559:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@559:  * accompanied this code).
jaroslav@559:  *
jaroslav@559:  * You should have received a copy of the GNU General Public License version
jaroslav@559:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@559:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@559:  *
jaroslav@559:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@559:  * or visit www.oracle.com if you need additional information or have any
jaroslav@559:  * questions.
jaroslav@559:  */
jaroslav@559: 
jaroslav@559: package java.lang;
jaroslav@559: 
jaroslav@559: import java.lang.annotation.*;
jaroslav@559: 
jaroslav@559: /**
jaroslav@559:  * A programmer assertion that the body of the annotated method or
jaroslav@559:  * constructor does not perform potentially unsafe operations on its
jaroslav@559:  * varargs parameter.  Applying this annotation to a method or
jaroslav@559:  * constructor suppresses unchecked warnings about a
jaroslav@559:  * <i>non-reifiable</i> variable arity (vararg) type and suppresses
jaroslav@559:  * unchecked warnings about parameterized array creation at call
jaroslav@559:  * sites.
jaroslav@559:  *
jaroslav@559:  * <p> In addition to the usage restrictions imposed by its {@link
jaroslav@559:  * Target @Target} meta-annotation, compilers are required to implement
jaroslav@559:  * additional usage restrictions on this annotation type; it is a
jaroslav@559:  * compile-time error if a method or constructor declaration is
jaroslav@559:  * annotated with a {@code @SafeVarargs} annotation, and either:
jaroslav@559:  * <ul>
jaroslav@559:  * <li>  the declaration is a fixed arity method or constructor
jaroslav@559:  *
jaroslav@559:  * <li> the declaration is a variable arity method that is neither
jaroslav@559:  * {@code static} nor {@code final}.
jaroslav@559:  *
jaroslav@559:  * </ul>
jaroslav@559:  *
jaroslav@559:  * <p> Compilers are encouraged to issue warnings when this annotation
jaroslav@559:  * type is applied to a method or constructor declaration where:
jaroslav@559:  *
jaroslav@559:  * <ul>
jaroslav@559:  *
jaroslav@559:  * <li> The variable arity parameter has a reifiable element type,
jaroslav@559:  * which includes primitive types, {@code Object}, and {@code String}.
jaroslav@559:  * (The unchecked warnings this annotation type suppresses already do
jaroslav@559:  * not occur for a reifiable element type.)
jaroslav@559:  *
jaroslav@559:  * <li> The body of the method or constructor declaration performs
jaroslav@559:  * potentially unsafe operations, such as an assignment to an element
jaroslav@559:  * of the variable arity parameter's array that generates an unchecked
jaroslav@559:  * warning.  Some unsafe operations do not trigger an unchecked
jaroslav@559:  * warning.  For example, the aliasing in
jaroslav@559:  *
jaroslav@559:  * <blockquote><pre>
jaroslav@559:  * &#64;SafeVarargs // Not actually safe!
jaroslav@559:  * static void m(List&lt;String&gt;... stringLists) {
jaroslav@559:  *   Object[] array = stringLists;
jaroslav@559:  *   List&lt;Integer&gt; tmpList = Arrays.asList(42);
jaroslav@559:  *   array[0] = tmpList; // Semantically invalid, but compiles without warnings
jaroslav@559:  *   String s = stringLists[0].get(0); // Oh no, ClassCastException at runtime!
jaroslav@559:  * }
jaroslav@559:  * </pre></blockquote>
jaroslav@559:  *
jaroslav@559:  * leads to a {@code ClassCastException} at runtime.
jaroslav@559:  *
jaroslav@559:  * <p>Future versions of the platform may mandate compiler errors for
jaroslav@559:  * such unsafe operations.
jaroslav@559:  *
jaroslav@559:  * </ul>
jaroslav@559:  *
jaroslav@559:  * @jls 4.7 Reifiable Types
jaroslav@559:  * @jls 8.4.1 Formal Parameters
jaroslav@559:  */
jaroslav@559: @Documented
jaroslav@559: @Retention(RetentionPolicy.RUNTIME)
jaroslav@559: @Target({ElementType.CONSTRUCTOR, ElementType.METHOD})
jaroslav@559: public @interface SafeVarargs {}