怎么用java创建一个空白的窗口

怎么用java创建一个空白的窗口

public class Demo_1 extends JFrame{

//JButton jb=null;
public static void main(String[] args) {
// TODO Auto-generated method stub
new Demo_1();

}
public Demo_1()
{
// jb=new JButton("我是按钮");
// this.add(jb);
this.setTitle("Hello,World!");
this.setSize(200,200);
this.setLocation(800, 200);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setVisible(true);

}
}

package com.yang.xu;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Frame extends JFrame{
private JPanel pnl;
public Frame()
{
pnl=new JPanel();
this.setSize(500, 400);
this.add(pnl);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setVisible(true);

}
public static void main(String[] args) {
new Frame();
}
}