Question

The documentation I’ve found doesn’t address this issue. I would think that calling cell.setCellStyle(a) and cell.setCellStyle(b) would completely overwrite style a and apply style b instead. However, it appears that it is applying both because the styles don’t conflict. Is this expected behavior or magic?

Answer 1

Well, here’s the source code for setCellStyle():

 public void setCellStyle(CellStyle style) {
     if(style == null) {
         if(_cell.isSetS()) _cell.unsetS();
     } else {
         XSSFCellStyle xStyle = (XSSFCellStyle)style;
         xStyle.verifyBelongsToStylesSource(_stylesSource);

         long idx = _stylesSource.putStyle(xStyle);
         _cell.setS(idx);
     }
 }

_cell is of type org.openxmlformats.schemas.spreadsheetml.x2006.main.CTCell and I couldn’t find the source code online. However, since the call to _cell.setS(idx) passes in just an index, the API doesn’t look rich enough to support merging of styles. I strongly suspect your second style has all the attributes you are seeing.