Java by API/org.eclipse.swt.events/PaintListener

implements PaintListener

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
public class MainClass {
  public static void main(String[] a) {
    final Display d = new Display();
    final Shell shell = new Shell(d);
    shell.setSize(250, 200);
    shell.setLayout(new FillLayout());
    Canvas drawingCanvas = new Canvas(shell, SWT.NONE);
    drawingCanvas.addPaintListener(new ArcExamplePaintListener());
    drawingCanvas.redraw();
    
    shell.open();
    while (!shell.isDisposed()) {
      if (!d.readAndDispatch())
        d.sleep();
    }
    d.dispose();
  }
}
class ArcExamplePaintListener implements PaintListener {
  public void paintControl(PaintEvent e) {
    Canvas canvas = (Canvas) e.widget;
    int x = canvas.getBounds().width;
    int y = canvas.getBounds().height;
    e.gc.setBackground(e.display.getSystemColor(SWT.COLOR_BLACK));
    e.gc.fillArc((x - 200) / 2, (y - 200) / 2, 200, 200, 0, 90);
  }
}