SafeVarargs (Java Platform SE 8 ) (original) (raw)

@Documented
@Retention(value=RUNTIME)
@Target(value={CONSTRUCTOR,METHOD})
public @interface SafeVarargs
A programmer assertion that the body of the annotated method or constructor does not perform potentially unsafe operations on its varargs parameter. Applying this annotation to a method or constructor suppresses unchecked warnings about a_non-reifiable_ variable arity (vararg) type and suppresses unchecked warnings about parameterized array creation at call sites.
In addition to the usage restrictions imposed by its @Target meta-annotation, compilers are required to implement additional usage restrictions on this annotation type; it is a compile-time error if a method or constructor declaration is annotated with a @SafeVarargs annotation, and either:

• the declaration is a fixed arity method or constructor
• the declaration is a variable arity method that is neitherstatic nor final.
  Compilers are encouraged to issue warnings when this annotation type is applied to a method or constructor declaration where:
• The variable arity parameter has a reifiable element type, which includes primitive types, Object, and String. (The unchecked warnings this annotation type suppresses already do not occur for a reifiable element type.)
• The body of the method or constructor declaration performs potentially unsafe operations, such as an assignment to an element of the variable arity parameter's array that generates an unchecked warning. Some unsafe operations do not trigger an unchecked warning. For example, the aliasing in

  @SafeVarargs // Not actually safe!
  static void m(List... stringLists) {
  Object[] array = stringLists;
  List tmpList = Arrays.asList(42);
  array[0] = tmpList; // Semantically invalid, but compiles without warnings
  String s = stringLists[0].get(0); // Oh no, ClassCastException at runtime!
  }

  leads to a `ClassCastException` at runtime.  

  Future versions of the platform may mandate compiler errors for such unsafe operations.
  Since:
  1.7
  See The Java™ Language Specification:
  4.7 Reifiable Types, 8.4.1 Formal Parameters, 9.6.3.7 @SafeVarargs

Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2025, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.