@Override
  public boolean seek(ExtendedCell cell) throws IOException {
    if (closed) {
      return false;
    }
    if (cell == null) {
      close();
      return false;
    }
    // restart the iterator from new key
    iter = getIterator(cell);
    // last is going to be reinitialized in the next getNext() call
    last = null;
    updateCurrent();
    return (current != null);
  }
Seek the scanner at or after the specified Cell.
@param cell seek value
@return true if scanner has values left, false if end of scanner
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/SegmentScanner.java