@SuppressWarnings("unchecked")
  private static Class<? extends CellComparator> getComparatorClass(String comparatorClassName)
    throws IOException {
    Class<? extends CellComparator> comparatorKlass;
    // for backward compatibility
    // We will force comparator class name to be "KeyValue$KVComparator" and
    // "KeyValue$MetaComparator" on 2.x although we do not use them on newer 2.x versions, for
    // maintaining compatibility while upgrading and downgrading between different 2.x versions. So
    // here on 3.x, we still need to check these two class names although the actual classes have
    // already been purged.
    if (
      comparatorClassName.equals("org.apache.hadoop.hbase.KeyValue$KVComparator")
        || comparatorClassName.equals("org.apache.hadoop.hbase.CellComparator")
    ) {
      comparatorKlass = InnerStoreCellComparator.class;
    } else if (
      comparatorClassName.equals("org.apache.hadoop.hbase.KeyValue$MetaComparator")
        || comparatorClassName.equals("org.apache.hadoop.hbase.CellComparator$MetaCellComparator")
        || comparatorClassName
          .equals("org.apache.hadoop.hbase.CellComparatorImpl$MetaCellComparator")
        || comparatorClassName.equals("org.apache.hadoop.hbase.MetaCellComparator")
    ) {
      comparatorKlass = MetaCellComparator.class;
    } else if (
      comparatorClassName.equals("org.apache.hadoop.hbase.KeyValue$RawBytesComparator")
        || comparatorClassName.equals("org.apache.hadoop.hbase.util.Bytes$ByteArrayComparator")
    ) {
      // When the comparator to be used is Bytes.BYTES_RAWCOMPARATOR, we just return null from here
      // Bytes.BYTES_RAWCOMPARATOR is not a CellComparator
      comparatorKlass = null;
    } else {
      // if the name wasn't one of the legacy names, maybe its a legit new kind of comparator.
      try {
        comparatorKlass = (Class<? extends CellComparator>) Class.forName(comparatorClassName);
      } catch (ClassNotFoundException e) {
        throw new IOException(e);
      }
    }
    return comparatorKlass;
  }
Returns the minor version of this HFile format
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/FixedFileTrailer.java