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");
    }
}