【Java】 GUI 画随机渐层颜色的圆圈

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) {
		
		Graphics2D g2d = (Graphics2D) g;
		
		int red = (int)(Math.random()*255);
		int green = (int)(Math.random()*255);
		int blue = (int)(Math.random()*255);
		Color startColor = new Color(red,green,blue);
		
		red = (int)(Math.random()*255);
		green = (int)(Math.random()*255);
		blue = (int)(Math.random()*255);
		Color endColor = new Color(red,green,blue);
		
		GradientPaint gradient = new GradientPaint(70,70,startColor,150,150,endColor);
		g2d.setPaint(gradient);
		g.fillOval(70, 70, 100, 100);
	}
}

抱歉，又是绿的

---

如果想添加一个按钮，使得不用关闭窗口就可以改变颜色

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

public class SystemUI implements ActionListener{ // 实现接口

	JButton button1 = new JButton("Change Circle");
	JFrame frame = new JFrame();
	
	public SystemUI() {
		
		
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setBounds(400, 300, 500, 300);
		frame.setVisible(true);
		
		
		frame.add(BorderLayout.SOUTH,button1);
		button1.addActionListener(this); // 向按钮注册
		
		DrawPanel dpanel = new DrawPanel();
		frame.add(BorderLayout.CENTER,dpanel);
		
	}
	
	public static void main(String[] args) {
		// TODO 自动生成的方法存根

		new SystemUI();
		
		
	}

	@Override
	public void actionPerformed(ActionEvent e) { // 实现接口上的方法
		// TODO 自动生成的方法存根
		//button1.setText("hello world");
		frame.repaint();
	}

}

class DrawPanel extends JPanel {

	private static final long serialVersionUID = 1L;

	public void paintComponent(Graphics g) {
		
		Graphics2D g2d = (Graphics2D) g;
		
		int red = (int)(Math.random()*255);
		int green = (int)(Math.random()*255);
		int blue = (int)(Math.random()*255);
		Color startColor = new Color(red,green,blue);
		
		red = (int)(Math.random()*255);
		green = (int)(Math.random()*255);
		blue = (int)(Math.random()*255);
		Color endColor = new Color(red,green,blue);
		
		GradientPaint gradient = new GradientPaint(70,70,startColor,150,150,endColor);
		g2d.setPaint(gradient);
		g.fillOval(70, 70, 100, 100);
	}
}