@Override
        public void visitClassDef(JCClassDecl tree) {
            List<JCTree> supertypes = List.nil();
            if (tree.getExtendsClause() != null) {
                supertypes = supertypes.prepend(tree.getExtendsClause());
            }
            if (tree.getImplementsClause() != null) {
                for (JCTree intf : tree.getImplementsClause()) {
                    supertypes = supertypes.prepend(intf);
                }
            }
            checkClass(tree.pos(), tree.sym, supertypes);
        }