src/share/classes/com/sun/tools/javac/comp/Attr.java

@@ -1144,11 +1144,12 @@
         result = null;
     }
 
     void checkAutoCloseable(DiagnosticPosition pos, Env<AttrContext> env, Type resource) {
         if (!resource.isErroneous() &&
-                types.asSuper(resource, syms.autoCloseableType.tsym) != null) {
+            types.asSuper(resource, syms.autoCloseableType.tsym) != null &&
+            !types.isSameType(resource, syms.autoCloseableType)) { // Don't emit warning for AutoCloseable itself
             Symbol close = syms.noSymbol;
             boolean prevDeferDiags = log.deferDiagnostics;
             Queue<JCDiagnostic> prevDeferredDiags = log.deferredDiagnostics;
             try {
                 log.deferDiagnostics = true;