java.lang.NullPointerException - 在AddCell方法中

Question

执行下面的代码：抛出Null Point异常------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- -------------------------------------------------- ----

package eCommerceLive;

import java.io.File;
import jxl.Workbook;
import jxl.write.WritableSheet;
import jxl.write.WritableWorkbook;
import jxl.write.Label;
import jxl.write.WriteException;


public class dataSheet {

static Workbook wbook;
static WritableWorkbook wwbCopy;
static String ExecutedTestCasesSheet;
static WritableSheet shSheet;

public void readExcel()
{
try{
wbook = Workbook.getWorkbook(new File("D:\\Automation\\testSampleData.xls"));
wwbCopy = Workbook.createWorkbook(new File("D:\\Automation\\testSampleDataCopy.xls"), wbook);
shSheet = wwbCopy.getSheet(0);
}
catch(Exception e)
{
    e.printStackTrace();
}
}

public void setValueIntoCell(String strSheetName,int iColumnNumber, int iRowNumber,String strData) throws WriteException
{
    WritableSheet wshTemp = wwbCopy.getSheet(strSheetName);
    Label labTemp = new Label(iColumnNumber, iRowNumber, strData);

    try {
        wshTemp.addCell(labTemp);
         } 
        catch (Exception e) 
        {

            System.out.println("Hello");
            e.printStackTrace();
        }
}

public void closeFile()
{
    try {
        // Closing the writable work book
        wwbCopy.write();
        wwbCopy.close();

        // Closing the original work book
        wbook.close();
    } catch (Exception e)

    {
        e.printStackTrace();
    }
}

public static void main(String[] args) throws WriteException
{
    dataSheet ds = new dataSheet();
    ds.readExcel();
    System.out.println("Hello");
    ds.setValueIntoCell("sheet1",5,1,"PASS");
    ds.setValueIntoCell("sheet1",5,2,"FAIL");
    ds.setValueIntoCell("sheet1",5,3,"PASS");
    ds.closeFile();
}

}