```java
public void updateStudent(){
//获取连接
Connection conn = DbUtil.getConnection();
//sql
String sql = "UPDATE Stdudent" +
" set user_name=?, sex=?, age=?, birthday=?, email=? "+
" where id=?";
//预编译
PreparedStatement ptmt = conn.prepareStatement(sql); //预编译SQL，减少sql执行
//传参
ptmt.setString(1, g.getUser_name());
ptmt.setInt(2, g.getSex());
ptmt.setInt(3, g.getAge());
ptmt.setDate(4, g.getBirthday());
ptmt.setInt(5, g.getId());
//执行
ptmt.execute();
DbUtil.close(ptmt,conn);
}
```