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

public class Gradation1 extends JPanel {
	public Gradation1() {
		setPreferredSize(new Dimension(256, 40));
	}
	
	@Override  
	public void paintComponent(Graphics g) {
		super.paintComponent(g);
		int scale = 4;
		int i;

		for (i = 0; i < 64; i++) {
			g.setColor(new Color(i * 4, 0, 255 - i * 4));
			g.fillRect(i * scale, 0, scale, scale * 10);
		} 
	}

	public static void main(String[] args) {
		SwingUtilities.invokeLater(() -> {
			JFrame frame = new JFrame("グラデーション");
			frame.add(new Gradation1());
			frame.pack();
			frame.setVisible(true);
			frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		});
	}
}