code: public static FsPermission createImmutable(short permission) {
      return new FsPermission(permission) {
        public FsPermission applyUMask(FsPermission umask) {
          throw new UnsupportedOperationException();
        }
        public void readFields(DataInput in) throws IOException {
          throw new UnsupportedOperationException();
        }
      };
    }
docs: Create an immutable {@link FsPermission} object.