Java Challenge on A Gradient Color Canvas

This is probably an elementary question. However, I have completed reading the 9th Chapter of Java Programming for the Absolute Beginner and have approached the Challenges section. I cannot quite get the progam to show a gradient from dark to light.

I mainly need help with my main method as this is where the problem is located.

The question asks:

"Create a Canvas that paints a gradient that's dark on one side and slowly gets lighter as it moves to the other side."

I do not know JFrame, Swing, Points, JPanels, BufferedImage, or GradientPaint.

Thank you very much for your time and cooperation reagrding this matter.

HERE IS THE CODE:

Code :

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import java.awt.*;
 
public class ColorfulShape extends GUIFrame {
 
	Canvas digital;
	public final static int MIN = 0,
							  MAX = 255;
	int r, g, b;
	Color paintr = new Color(0, 0, 0);
 
	public ColorfulShape(int r, int g, int b) {
		super("Colorful Shape");
		r = r >= MIN && r <= MAX ? r : MIN;
		g = g >= MIN && g <= MAX ? g : MIN;
		b = r >= MIN && b <= MAX ? b : MIN;
		digital = new Canvas();
		digital.setBackground(new Color(r, g, b));
		digital.setSize(200, 150);
		add(digital, BorderLayout.CENTER);
 
		pack();
		setVisible(true);
	}
 
 
	public static void main(String args[]) {
new ColorfulShape(0, 0, 0);
}
	public void paint(Graphics g) {
	for(int i=MIN; i<=MAX; i++) {
		paintr = paintr.brighter();
	}
	}
}

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Quote:

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I do not know JFrame, Swing, Points, JPanels, BufferedImage, or GradientPaint.

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Take a look at the tutorial:
Trail: Creating a GUI With JFC/Swing (The Java™ Tutorials)