Primo approccio alla grafica su Android.

E così abbiamo disegnato un cerchio...

Ora disegno la bandiera del Giappone...

        @Override
        public void onDraw(Canvas canvas){
         super.onDraw(canvas);
         int x=getWidth();
         int y=getHeight();
         int radius;
         radius=100;
         Paint paint=new Paint();
         paint.setStyle(Paint.Style.FILL);
         paint.setColor(Color.RED);
         canvas.drawCircle(x/2, y/2, radius, paint);
         
        }

Cerchi concentrici...

        @Override
        public void onDraw(Canvas canvas){
         super.onDraw(canvas);
         int x=getWidth();
         int y=getHeight();
         Paint paint=new Paint();
         paint.setStyle(Paint.Style.FILL);
         paint.setColor(Color.GREEN);
         canvas.drawCircle(x/2, y/2, 100, paint);
         paint.setColor(Color.RED);
         canvas.drawCircle(x/2, y/2, 80, paint);
         paint.setColor(Color.YELLOW);
         canvas.drawCircle(x/2, y/2, 60, paint);
         paint.setColor(Color.BLUE);
         canvas.drawCircle(x/2, y/2, 40, paint);
         paint.setColor(Color.CYAN);
         canvas.drawCircle(x/2, y/2, 20, paint);
         
        }