遍历 Vector 的两种方法：
Iterator iter = v.iterator();
while(iter.hasNext()){
StudentVo value = (StudentVo)iter.next();
System.out.println(value);
}
Enumeration enu = v.elements();
while(enu.hasMoreElements()){
StudentVo value = (StudentVo)enu.nextElement();
System.out.println(value);
}