Question

What does index mean in getMergedRegion?

Apache’s HSSFSheet documentation does not explicitly describe what the index parameter means.

Answer 1

From the freely available source downloadable here http://poi.apache.org/download.html we have …

/**
 * @return the merged region at the specified index
 */
public CellRangeAddress getMergedRegion(int index) {
    return _sheet.getMergedRegionAt(index);
}

When we drill down to getMergedRegionAt we find

public CellRangeAddress getMergedRegionAt(int index) {
    //safety checks
    MergedCellsTable mrt = getMergedRecords();
    if (index >=  mrt.getNumberOfMergedRegions()) {
        return null;
    }
    return mrt.get(index);
}

Here we can see that there is a MergedCellsTable this would indicate that each worksheet has a data structure that maintains a list of the Merged Cells in a WorkSheet.

From reviewing the code the index references the specific MergedRegion whose CellRangeAddress was required in the context of having many regions.

You could log that as a doc bug or submit a patch to improve the JavaDoc.