code: public static boolean isNonPublicProxyClass(Class<?> cls) {
          String name = cls.getName();
          int i = name.lastIndexOf('.');
          String pkg = (i != -1) ? name.substring(0, i) : "";
  
          // NOTE: Android creates proxies in the "default" package (and not com.sun.proxy), which
          // makes this check imprecise. However, this function is only ever called if there's
          // a security manager installed (which is the never case on android).
          return Proxy.isProxyClass(cls) && !pkg.isEmpty();
      }
docs: Test if the given class is a proxy class that implements
  non-public interface.  Such proxy class may be in a non-restricted
  package that bypasses checkPackageAccess.