for exapmle...

InputStream is = new FileInputStream("src/test/resources/Test.xls");
HSSFWorkbook wb = new HSSFWorkbook(is);
HSSFSheet sheet = wb.getSheetAt(0); // 2rows in this sheet
System.out.println(sheet.getFirstRowNum()); // 0
System.out.println(sheet.getLastRowNum());  // 1
//remove all rows
for(int i= sheet.getLastRowNum(); i >= sheet.getFirstRowNum(); i--){
    HSSFRow row = sheet.getRow(i);
    sheet.removeRow(row);
}
System.out.println(sheet.getFirstRowNum()); // -1
System.out.println(sheet.getLastRowNum());  // -1
sheet.createRow(0);
sheet.createRow(1);
System.out.println(sheet.getFirstRowNum()); // -1
System.out.println(sheet.getLastRowNum());  // 1