【Java】 GUI 在黑色背景画上随机色彩的圆圈

import javax.swing.*;
import java.awt.*;

public class SystemUI{ 
	
	public SystemUI() {
		
		JFrame frame = new JFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setBounds(400, 300, 500, 300);
		frame.setVisible(true);
		
		DrawPanel dpanel = new DrawPanel();
		frame.add(dpanel);
		
	}
	
	public static void main(String[] args) {
		// TODO 自动生成的方法存根
		new SystemUI();
		
	}

}

class DrawPanel extends JPanel {

	private static final long serialVersionUID = 1L;

	public void paintComponent(Graphics g) {
		
		g.fillRect(0, 0, getWidth(), getHeight());
		
		int red = (int)(Math.random()*255);
		int green = (int)(Math.random()*255);
		int blue = (int)(Math.random()*255);
		
		Color randomColor = new Color(red,green,blue);
		g.setColor(randomColor);
		g.fillOval(70, 70, 100, 100);
	}
}