How to use setLocked()? It won't want to work

[Marek Wozny]

Hello,
 
how does I use the setLocked() method correctly?
What does I have to do with the excelfile? 
Are there any options I have to prepare the excelfile with, before I
read the file?
 
here is a small codesnip:
 
       POIFSFileSystem fs = new POIFSFileSystem(new
FileInputStream(tempFilePath));
       HSSFWorkbook wb2 = new HSSFWorkbook(fs);
       HSSFSheet sheet2 = wb2.getSheetAt(0);
       
        //sheet2.setProtect(true);  //   <--- throws a Nullpointer if
uncommented, why?
       //System.out.println("PROTECTED: " + sheet2.getProtect());
       
       HSSFRow row2 = sheet2.getRow(0);
       HSSFCell cell2 = null;
       
       HSSFCellStyle cs = wb2.createCellStyle();
       cs.setLocked(true); // <-- this should set the file locked, isn't
it?
 
       cell2 = row2.getCell((short) cols);
          if (cell2 == null)
          { 
           cell2 = row2.createCell((short) cols);
           cell2.setCellStyle(cs);
           cell2.setCellValue("not entered");
          }//if        
 
 
       FileOutputStream fileOut = new
FileOutputStream(tempFilePath+"workbook2.xls");
       wb2.write(fileOut);
       fileOut.close(); 
 
 
I hope you are able to help me.
 
regards,
marek