```java
//增加
public void addStudent(Student g) throws SQLException {
//获取连接
Connection conn = DbUtil.getConnection();
//sql
String sql = "INSERT INTO student(user_name, sex, age, birthday )"
+"values("+"?,?,?,? )";
//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.setString(4, g.getBirthday());
//执行
ptmt.execute();
DbUtil.close(ptmt,conn);
}
```