java swing 启动一个简单的窗体

import javax.swing.*;
import java.awt.event.*;
public class Demo extends JFrame
{
public Demo(String title){
this.setTitle(title);//设置窗体标题
this.setBounds(350,350,350,300);//设置窗体尺寸
this.setVisible(true);//显示窗体
this.addWindowListener(new WindowAdapter(){//添加窗体关闭事件
public void windowClosing(WindowEvent ev){
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
}
});
}

public static void main(String[]args){
new Demo("Test");
}
}