DragonCurve.java

/**
 * Dragon Curve implementation.
 */
public class DragonCurve {
    private static final int ORDER = 14;
    private static final double STEP = 0.002;

    public static void main(String[] args) {
        StdDraw.setCanvasSize(900, 900);
        StdDraw.setXscale(0, 1);
        StdDraw.setYscale(0, 1);

        // Build string using L-system
        String seq = "F";

        for (int i = 0; i < ORDER; i++) {
            StringBuilder next = new StringBuilder();
            for (char c : seq.toCharArray()) {
                if (c == 'F') next.append("F+G");
                else if (c == 'G') next.append("F-G");
                else next.append(c);
            }
            seq = next.toString();
        }

        double x = 0.5, y = 0.5;
        double angle = 0;

        for (char c : seq.toCharArray()) {
            if (c == 'F' || c == 'G') {
                double x2 = x + STEP * Math.cos(angle);
                double y2 = y + STEP * Math.sin(angle);
                StdDraw.line(x, y, x2, y2);
                x = x2;
                y = y2;
            } else if (c == '+') {
                angle += Math.PI / 2;
            } else if (c == '-') {
                angle -= Math.PI / 2;
            }
        }
    }
}