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 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} 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 * @SafeVarargs // Not actually safe! 70 * static void m(List<String>... stringLists) { 71 * Object[] array = stringLists; 72 * List<Integer> 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}) 93 public @interface SafeVarargs {} 94