Using Icon and myIcon

I am practicing using Icon and myIcon and am getting an error saying that myIcon must be defined in its own file. I am pretty sure I defined it within the code and am confused what I did wrong.

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

public class TestIcon {
    public static void main(String[] args) {
        myIcon icn = new myIcon(40,50);
        JOptionPane.showMessageDialog(null, "Hello World!", "Message", JOptionPane.INFORMATION_MESSAGE, icn);
    }
}

public class myIcon implements Icon{
    private int width;
    private int height;

    public myIcon(int width, int height) {
        this.width=width;
        this.height=height;
    }
    public int getIconWidth(){
        return width;
    }
    public int getIconHeight(){
        return height;
    }
    public void paintIcon(Component c, Graphics g, int x, int y){
        Graphics2D g2 = (Graphics2D) g;
        Ellipse2D.Double ellipse = new Ellipse2D.Double(x,y,width, height);

        g2.setColor(Color.RED);
        g2.fill(ellipse);
    }
 }