JFrame类的小小问题
非常小的问题，为什么我调用JFrame类的时候，这个窗口出来的时候没有任何组件，然后随意调大或者调小窗口，组件就都出来了。很奇怪
类代码：public class Change_password extends JFrame implements ActionListener{
/**
* 
*/
private static final long serialVersionUID = 1L;
Userinfo uinfo;
JLabel Lpassword = new JLabel("原密码");
JLabel Lnew_password = new JLabel("新密码");
JLabel Lnew_password2 = new JLabel("新密码确认");
JTextField password = new JTextField();
JPasswordField new_password = new JPasswordField();
JPasswordField new_password2 = new JPasswordField();
JButton ok = new JButton("提交");
JButton back = new JButton("返回");
JButton qingkong = new JButton("清空");
Panel p;
int uid2;
 public Change_password(int uid){
 uid2 = uid;
 p = new Panel(new GridLayout(3, 3));
 p.add(Lpassword);
 p.add(password);
 p.add(ok);
 p.add(Lnew_password);
 p.add(new_password);
 p.add(qingkong);
 p.add(Lnew_password2);
 p.add(new_password2);
 p.add(back);
 this.getContentPane().add(p,BorderLayout.CENTER);
 
 ok.addActionListener(this);
 back.addActionListener(this);
 qingkong.addActionListener(this);
 
 setVisible(true);
 setSize(250,150);
 //setLocationRelativeTo(this);
 setDefaultCloseOperation(3);
 }
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
if(e.getSource()== ok){
  //调用修改方法
}
if(e.getSource()== back){
setVisible(false);
uinfo = new Userinfo(uid2);
}
if(e.getSource() == qingkong){
password.setText(null);
new_password.setText(null);
new_password2.setText(null);
}
}
}

------解决方案--------------------

------解决方案--------------------
可能是组件大小导致的问题，再加入所有组件之后，写一句
 pack();
------解决方案--------------------
修改后的程序(红色是修改后的地方,这两行颠倒了):
package com.jst;

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

public class Change_password extends JFrame implements ActionListener {
/**
* 
*/
public static void main(String[] args) {
new Change_password(1);
}
private static final long serialVersionUID = 1L;

// Userinfo uinfo;
JLabel Lpassword = new JLabel("原密码");

JLabel Lnew_password = new JLabel("新密码");

JLabel Lnew_password2 = new JLabel("新密码确认");

JTextField password = new JTextField();

JPasswordField new_password = new JPasswordField();

JPasswordField new_password2 = new JPasswordField();

JButton ok = new JButton("提交");

JButton back = new JButton("返回");

JButton qingkong = new JButton("清空");

Panel p;

int uid2;

public Change_password(int uid) {
uid2 = uid;
p = new Panel(new GridLayout(3, 3));
p.add(Lpassword);
p.add(password);
p.add(ok);
p.add(Lnew_password);
p.add(new_password);
p.add(qingkong);
p.add(Lnew_password2);
p.add(new_password2);
p.add(back);
this.getContentPane().add(p, BorderLayout.CENTER);

ok.addActionListener(this);
back.addActionListener(this);