java利用GUI进行图形绘制完成下列任务

利用对话框，输入数字，依靠类Graphics中的方法drawOval画出对应数字的同心圆环

package com;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class DrawDemo extends JFrame implements ActionListener{

    JButton btnSelect;
    int level=10;
    
    public DrawDemo() {
        super("绘图Demo");
        
        btnSelect = new JButton("输入数量");
        btnSelect.addActionListener(this);
        
        add(btnSelect,BorderLayout.NORTH);
        setSize(700,700);
        setVisible(true);
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }
    
    @Override
    public void actionPerformed(ActionEvent e) {
        
        if(e.getSource() == btnSelect) {
            //用输入对话框获取用户的值
            String s=JOptionPane.showInputDialog("请输入（1~50)的数字", 10);
            //点击了取消按钮
            if(s==null) {
                return;
            }
            level = Integer.parseInt(s);
            repaint();
        }
    }
    @Override
    public void paint(Graphics g) {
        super.paint(g);
        //画图
        int r = 50;
        int x0=getSize().width/2;
        int y0=getSize().height/2;//圆心
        
        for(int i=0;i<level;i++) {
            r += 10;
            g.setColor(Color.RED);
            g.drawOval(x0,y0,r,r);//椭圆
        }
    }
    public static void main(String[] args) {
        new DrawDemo();
    }
}

这个也没什么思路，会用swing写GUI的应该就搞定了，自己弄吧