private final boolean _next() throws IOException {
      // Small method so can be inlined. It is a hot one.
      if (blockBuffer.remaining() <= 0) {
        return positionForNextBlock();
      }

      // We are still in the same block.
      readKeyValueLen();
      return true;
    }
Set our selves up for the next 'next' invocation, set up next block.
@return True is more to read else false if at the end.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderImpl.java