code: public static boolean isInitialConstructor(JCTree tree) {
          JCMethodInvocation app = firstConstructorCall(tree);
          if (app == null) return false;
          Name meth = name(app.meth);
          return meth == null || meth != meth.table.names._this;
      }
docs: Is this a constructor whose first (non-synthetic) statement is not
  of the form this(...)?