弹窗 （默认就有窗口关闭事件）

package cn.rushangw.lesson04;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

//主窗口
public class DialogDemo extends JFrame {

    public void init(){
        setVisible(true);
        setBounds(1,1,400,400);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        //放东西，容器
        Container contentPane = getContentPane();
        //绝对定位
        contentPane.setLayout(null);

        //按钮
        JButton jButton = new JButton("点击弹出一个对话框");
        jButton.setBounds(30,30,200,50);

        //监听事件
        jButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                //弹出窗口
                new MyDialogDemo();
            }
        });

        //点击这个按钮弹出对话框
        contentPane.add(jButton);
    }
    public static void main(String[] args) {
        new DialogDemo().init();
    }
}

//弹窗的窗口
class MyDialogDemo extends JDialog{
    public MyDialogDemo() {
        setVisible(true);
        setBounds(100,100,500,500);
        //setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        Container container = getContentPane();
        container.setLayout(null);

        container.add(new Label("什么是快乐星球？"));
    }
}