Question: I m not able to edit the existing excel sheet using jxl.
It always creates a new one.
Can anyone please help me out with it.
Please give a small sample code.

Answer: 
I know that this is quite an old question, but if anyone will encounter the same problem, then to preserve the correct formatting (font type, colouring, etc. )
you should save the cell format before casting it to Label, and then force the cell to the previous formatting. 
Code:

```
CellFormat cfm = cell.getCellFormat();
Label l = (Label) cell; 
l.setString("modified cell");
cell.setCellFormat(cfm);

```
```
//there is god example of it, you can copy in ur project and check it out, to 
//understand how  it works

Workbook wk = Workbook.getWorkbook(new File("ex.xls"));
// 
WritableWorkbook wkr = Workbook.createWorkbook(new File("modifed.xls"), wk);
/* second line makes copy of wk excel file object /creates a readable spreadsheet.
both are now similar and i can Modify exiting wkr spreadsheets */

 //next 2 line retrieve sheet number 0  and cell (1,1)

 WritableSheet getsht = wkr.getSheet(0);
 WritableCell getcl = getsht.getWritableCell(1, 1);

 //making own font 

WritableFont ft = new WritableFont(WritableFont.ARIAL, 20 , WritableFont.BOLD, true , UnderlineStyle.SINGLE); 
//making Format, which uses font
WritableCellFormat   form   =   new WritableCellFormat( ft);

Number nb = ( Number ) getcl ;          
nb.setCellFormat( form );    

wkr.write();
wkr.close();

```