Jexcel - Updating an excel with data

I've tried using Jexcel

to update an existing excel sheet as discussed in the Vogella tutorial.

Issue here is the data already present in the existing excel sheet is wiped out with the newly written excel data.

For example if I've this in the excel

<table>
<tr>
<td>1</td> <td>2 </td>
</tr>
<tr>
<td>3</td> <td>4 </td>
</tr>
<table>

and I want to add data to the new cell next to 2 and 4, like

<table>
<tr>
<td>1</td> <td>2 </td> <td>X </td>
</tr>
<tr>
<td>3</td> <td>4 </td> <td>Y </td>
</tr>
<table>

after the write program executed this is what I get

<table>
<tr>
<td> </td> <td>  </td> <td>X </td>
</tr>
<tr>
<td> </td> <td>  </td> <td>Y </td>
</tr>
<table>

Label label;
label = new Label(column, row, s, times);
sheet.addCell(label);

This is adding the cell at the specified column and row but wiping out the rest of the excel data.

How can I add data to the existing excel keeping the data?

Following is the program(Reference: Vogella). Excel sheet already has data in 20 rows and first 2 columns, am trying to add data on the 3rd column for 20 rows package excel;

import java.io.File;
import java.io.IOException;
import java.util.Locale;

import jxl.CellView;
import jxl.Workbook;
import jxl.WorkbookSettings;
import jxl.format.UnderlineStyle;
import jxl.write.Label;
import jxl.write.WritableCellFormat;
import jxl.write.WritableFont;
import jxl.write.WritableSheet;
import jxl.write.WritableWorkbook;
import jxl.write.WriteException;
import jxl.write.biff.RowsExceededException;

public class WriteExcel {

    private WritableCellFormat timesBoldUnderline;
    private WritableCellFormat times;
    private String inputFile;

    public void setOutputFile(String inputFile) {
        this.inputFile = inputFile;
    }

    public void write() throws IOException, WriteException {
        File file = new File(inputFile);
        WorkbookSettings wbSettings = new WorkbookSettings();

        wbSettings.setLocale(new Locale("en", "EN"));

        WritableWorkbook workbook = Workbook.createWorkbook(file, wbSettings);
        workbook.createSheet("Report", 0);
        WritableSheet excelSheet = workbook.getSheet(0);
        createLabel(excelSheet);
        createContent(excelSheet);

        workbook.write();
        workbook.close();
    }

    private void createLabel(WritableSheet sheet) throws WriteException {
        // Lets create a times font
        WritableFont times10pt = new WritableFont(WritableFont.TIMES, 10);
        // Define the cell format
        times = new WritableCellFormat(times10pt);
        // Lets automatically wrap the cells
        times.setWrap(true);

        // Create create a bold font with unterlines
        WritableFont times10ptBoldUnderline = new WritableFont(
                WritableFont.TIMES, 10, WritableFont.BOLD, false,
                UnderlineStyle.SINGLE);
        timesBoldUnderline = new WritableCellFormat(times10ptBoldUnderline);
        // Lets automatically wrap the cells
        timesBoldUnderline.setWrap(true);

        CellView cv = new CellView();
        cv.setFormat(times);
        cv.setFormat(timesBoldUnderline);
        cv.setAutosize(true);

    }

    private void createContent(WritableSheet sheet) throws WriteException,
            RowsExceededException {

        Integer salary = 1000;
        // Now a bit of text
        for (int i = 0; i < 20; i++) {
            // third column
            addLabel(sheet, 2, i, salary.toString());

            // WritableCell cell = sheet.getWritableCell(2, i);
            // if (cell.getType() == CellType.LABEL) {
            // Label l = (Label) cell;
            // l.setString("modified cell");
            // }
            salary += 1000;
        }

    }

    private void addLabel(WritableSheet sheet, int column, int row, String s)
            throws WriteException, RowsExceededException {
        Label label;
        label = new Label(column, row, s, times);
        sheet.addCell(label);
    }

    public static void main(String[] args) throws WriteException, IOException {
        WriteExcel test = new WriteExcel();
        test.setOutputFile("c:/temp/lars.xls");
        test.write();
        System.out
                .println("Please check the result file under c:/temp/lars.xls ");
    }
}