8061549: Disallow _ as a one-character identifier

Underscore is no longer a one-charater identifier with -source 9

Reviewed-by: mcimadamore, jjg

langtools/test/tools/javac/lambda/UnderscoreAsIdent.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2013, 2014, 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=UnderscoreAsIdent8.out -source 8 -Xlint:-options -XDrawDiagnostics -Werror UnderscoreAsIdent.java
+ * @compile/fail/ref=UnderscoreAsIdent9.out -XDrawDiagnostics -Werror UnderscoreAsIdent.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 _;
+        }
+    }
+}