Question

这段代码为什么运行会左上角还出现一个窗口

package ui;
import javax.swing.*;

import Dao.StudentDao;
import Dao.UserDao;

import java.awt.*;
import java.awt.event.*;
import java.sql.ResultSet;
public class RegisterJFrame extends JFrame{

public RegisterJFrame(){
JFrame jf = new JFrame("新建");
jf.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);// 关闭
jf.setSize(300, 400); // 窗口大小
jf.setLocation(200, 200); // 窗口位置
jf.setResizable(false);
JPanel pan = new JPanel();
jf.add(pan);
jf.setVisible(true);
pan.setLayout(null);
Font f = new Font("宋体", Font.BOLD, 14);

JLabel person_id = new JLabel("ID");
person_id.setBounds(20,0,100,100);
pan.add(person_id);
person_id.setFont(f);
JTextField tf_account = new JTextField(10);
tf_account.setBounds(100, 40, 150, 25);
pan.add(tf_account);

JLabel person_name = new JLabel("姓名");
person_name.setBounds(20, 40, 100, 100);
pan.add(person_name);
person_name.setFont(f);

JTextField name = new JTextField(20);
name.setBounds(100, 80, 150, 25);
pan.add(name);

JLabel Person_sex = new JLabel("性别");
Person_sex.setBounds(20, 80, 100, 100);
pan.add(Person_sex);
Person_sex.setFont(f);

JTextField sex = new JTextField(20);
sex.setBounds(100, 120, 150, 25);
pan.add(sex);

JLabel Person_Birthday = new JLabel("生日");
Person_Birthday.setBounds(20, 120, 100, 100);
pan.add(Person_Birthday);
Person_Birthday.setFont(f);

JTextField birthday = new JTextField(20);
birthday.setBounds(100, 160, 150, 25);
pan.add(birthday);

JLabel Person_balance = new JLabel("余额");
Person_balance.setBounds(20,160, 100, 100);
pan.add(Person_balance);
Person_balance.setFont(f);

JTextField balance = new JTextField(20);
balance.setBounds(100, 200, 150, 25);
pan.add(balance);

JButton register = new JButton("新建");
register.setBounds(100, 240, 75, 30);
pan.add(register);

JButton qx = new JButton("取消");
qx.setBounds(175, 240, 75, 30);
pan.add(qx);
}

public static void main(String[] args) {
// TODO Auto-generated method stub
new RegisterJFrame().setVisible(true);
}

}

Answer 1

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