看下面java代码，有关Java与Excel的问题，盼高手解答！！！

改变“row = sheet.createRow(0)”里括号里的值，多次运行为什么只能往workbook.xls插入一条数据？怎样插入多条数据？
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;

import org.apache.poi.hslf.model.Sheet;
import org.apache.poi.hssf.model.Workbook;
import org.apache.poi.hssf.record.formula.functions.Row;
import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFRow;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;

public class Aa {

public static void main(String[] args) {
HSSFWorkbook wb = new HSSFWorkbook();
HSSFSheet sheet = wb.createSheet();
HSSFRow row = sheet.createRow(0);
row.createCell((short) 0).setCellValue(0);
row.createCell((short) 1).setCellValue(1);
row.createCell((short) 2).setCellValue(2);
row.createCell((short) 3).setCellValue("value");
row.cre

public class ClientUI extends JPanel {
/**
*
* @param title 要写的文件的表头
* @param datas 要写入的文件内容 （是一个数据的集合）
* @param path 要写入文件的路径
* @throws Exception
*/
private void writeToXls(String[] title,List<Object[]> datas,String path) throws Exception {

OutputStream fos = null;
try {
File f = new File(path);
fos = new FileOutputStream(f);
HSSFWorkbook wb = new HSSFWorkbook();
HSSFSheet sheet = wb.createSheet();
HSSFRow titlerow=sheet.getRow(0);
for (short i = 0; i < title.length; i++) {
HSSFCell cell=titlerow.createCell(i);
cell.setCellValue(title[i]);
}
for (int i = 0; i < datas.size(); i++) {
HSSFRow row=sheet.createRow(i+1);
Object[] obj=datas.get(i);
for (short j = 0; j < obj.length; j++) {
HSSFCell cell=row.createCell(j);
cell.setCellValue(obj[j].toString());
}