public class SlidingSquare {
    public static void main(String[] args) {
        double xCenter = 0;
        double yCenter = 0.5;
        double sideLength = 0.1;
        PennDraw.setCanvasSize(400, 400);
        PennDraw.enableAnimation(30);
        while (true) {
            PennDraw.clear();
            PennDraw.square(xCenter, yCenter, sideLength);
            xCenter = xCenter + 0.005;
            if (xCenter > 1.1) {
                xCenter = 0;
            }
            PennDraw.advance();
        }
    }
}