code: private void seekToRestartPosition(int restartPosition)
      {
          checkPositionIndex(restartPosition, restartCount, "restartPosition");
  
          // seek data readIndex to the beginning of the restart block
          int offset = restartPositions.getInt(restartPosition * SIZE_OF_INT);
          data.setPosition(offset);
  
          // clear the entries to assure key is not prefixed
          nextEntry = null;
  
          // read the entry
          nextEntry = readEntry(data, null);
      }
docs: Seeks to and reads the entry at the specified restart position.
  <p/>
  After this method, nextEntry will contain the next entry to return, and the previousEntry will be null.