--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/diags/examples/UnderscoreAsIdentifier.java	Fri Jan 18 15:38:14 2013 +0000
@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2013, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+// key: compiler.warn.underscore.as.identifier
+
+class UnderscoreAsIdentifier {
+    String _ = null;
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/lambda/WarnUnderscoreAsIdent.java	Fri Jan 18 15:38:14 2013 +0000
@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2013, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @summary Check usages of underscore as identifier generate warnings
+ * @compile/fail/ref=WarnUnderscoreAsIdent.out -XDrawDiagnostics -Werror WarnUnderscoreAsIdent.java
+ */
+package _._;
+
+import _._;
+
+class _ {
+    String _ = null;
+    void _(String _) { }
+    void testLocal() {
+        String _ = null;
+    }
+    void testFor() {
+        for (int _ = 0; _ < 10; _++);
+    }
+    void testTry() {
+        try { } catch (Throwable _) { }
+    }
+    void testLabel() {
+        _:
+        for (;;) {
+            break _;
+        }
+        _:
+        for (;;) {
+            continue _;
+        }
+    }
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/test/tools/javac/lambda/WarnUnderscoreAsIdent.out	Fri Jan 18 15:38:14 2013 +0000
@@ -0,0 +1,20 @@
+WarnUnderscoreAsIdent.java:29:9: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:29:11: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:31:8: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:31:10: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:33:7: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:34:12: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:35:10: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:35:19: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:37:16: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:40:18: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:40:25: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:40:33: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:43:34: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:46:9: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:48:19: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:50:9: compiler.warn.underscore.as.identifier
+WarnUnderscoreAsIdent.java:52:22: compiler.warn.underscore.as.identifier
+- compiler.err.warnings.and.werror
+1 error
+17 warnings