7011326: Add informative example to @SafeVarargs type or language discussion
Reviewed-by: mcimadamore, mduigou
--- a/jdk/src/share/classes/java/lang/SafeVarargs.java Mon May 02 20:17:18 2011 +0100
+++ b/jdk/src/share/classes/java/lang/SafeVarargs.java Fri May 06 17:06:25 2011 -0700
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -32,7 +32,7 @@
* constructor does not perform potentially unsafe operations on its
* varargs parameter. Applying this annotation to a method or
* constructor suppresses unchecked warnings about a
- * <i>non-reifiable</i> variable-arity (vararg) type and suppresses
+ * <i>non-reifiable</i> variable arity (vararg) type and suppresses
* unchecked warnings about parameterized array creation at call
* sites.
*
@@ -41,11 +41,10 @@
* additional usage restrictions on this annotation type; it is a
* compile-time error if a method or constructor declaration is
* annotated with a {@code @SafeVarargs} annotation, and either:
-
* <ul>
- * <li> the declaration is a fixed-arity method or constructor
+ * <li> the declaration is a fixed arity method or constructor
*
- * <li> the declaration is a variable-arity method that is neither
+ * <li> the declaration is a variable arity method that is neither
* {@code static} nor {@code final}.
*
* </ul>
@@ -55,15 +54,28 @@
*
* <ul>
*
- * <li> The variable-arity parameter has a reifiable element type,
+ * <li> The variable arity parameter has a reifiable element type,
* which includes primitive types, {@code Object}, and {@code String}.
* (The unchecked warnings this annotation type suppresses already do
* not occur for a reifiable element type.)
*
* <li> 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.
+ * 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
+ *
+ * <blockquote><pre>
+ * @SafeVarargs // Not actually safe!
+ * static void m(List<String>... stringLists) {
+ * Object[] array = stringLists;
+ * List<Integer> tmpList = Arrays.asList(42);
+ * array[0] = tmpList; // Semantically invalid, but compiles without warnings
+ * String s = stringLists[0].get(0); // Oh no, ClassCastException at runtime!
+ * }
+ * </pre></blockquote>
+ *
+ * leads to a {@code ClassCastException} at runtime.
*
* <p>Future versions of the platform may mandate compiler errors for
* such unsafe operations.