If the following code is executed, subsequent calls to dataFormat.getFormat() 
will cause all the formated cells to have the last requested format instead of 
the format that was set on them in previous call to dataFormat.getFormat() 


        HSSFWorkbook wb = new HSSFWorkbook();
        HSSFSheet sheet = wb.createSheet("new sheet");

        HSSFRow row = sheet.createRow((short)0);

        short iFormat = 0;

        HSSFDataFormat dataFormat = wb.createDataFormat(); 

        HSSFCell cell = row.createCell((short)0);
        iFormat = dataFormat.getFormat("000000%");
        cell.getCellStyle().setDataFormat(iFormat);         
        cell.setCellFormula("1/"+ String.valueOf(iFormat));
        //cell.setCellValue("1");


        //HSSFCell first_cell = cell;
        
        cell = row.createCell((short)1);
        iFormat = dataFormat.getFormat("00000%");
        cell.getCellStyle().setDataFormat(iFormat);         
        cell.setCellFormula("1/"+ String.valueOf(iFormat));
        //cell.setCellValue("1");


        cell = row.createCell((short)2);
        iFormat = dataFormat.getFormat("0000%");
        cell.getCellStyle().setDataFormat(iFormat);         
        cell.setCellFormula("1/"+ String.valueOf(iFormat));
        //cell.setCellValue("1");

        //iFormat = dataFormat.getFormat("000000%");
        //first_cell.getCellStyle().setDataFormat(iFormat);         


        FileOutputStream fileOut = new FileOutputStream("workbook.xls");
        wb.write(fileOut);
        fileOut.close();


Also using cell.setCellValue("1") looks like it is not working as it will not 
cause the cell to effectivelly use any of the specified formats (set on the 
cell before or after call to cell.setCellValue()), but that is another story...
Therefore in this example I am using cell.setCellFormula() with index number of 
the format written into the sheet.


If the code

        //HSSFCell first_cell = cell;
         .
         .
         .
        //iFormat = dataFormat.getFormat("000000%");
        //first_cell.getCellStyle().setDataFormat(iFormat);         

you will see format of all the touched cells set to 000000%.