why does this paint twice?

[Schwartz, Cynthia L]

I am writing a custom control and want to understand why this is painting 
twice. Complete code below.

Thanks,
Cynthia

public class PaintTest extends Application.Adapter {
    private Window window = null;
    private Waveform waveform = null;

    @Override
    public void startup(Display display, Map<String, String> properties) {
        window = new Window();
                waveform = new Waveform();
                window.setContent(waveform);
        window.setMaximized(true);
        window.open(display);
    }

    @Override
    public boolean shutdown(boolean optional) {
        if (window != null) {
            window.close();
        }

        return false;
    }

    public static void main(String[] args) {
        DesktopApplicationContext.main(PaintTest.class, args);
    }

}

package painttest;

import java.awt.Graphics2D;
import org.apache.pivot.wtk.Panel;

public class Waveform extends Panel
{
       @Override
        public void paint(Graphics2D graphics)
    {
                System.out.println("Painting");
}
}