Tree.java

/******************************************************************************
 *  Compilation:  javac Tree.java
 *  Execution:    java Tree n
 *  Dependencies: StdDraw.java
 *
 *  Plot a tree fractal.
 *
 *  % java Tree 9
 *
 ******************************************************************************/


public class Tree {

    public static void tree(int n, double x, double y, double a, double branchRadius) {
        double bendAngle   = Math.toRadians(15);
        double branchAngle = Math.toRadians(37);
        double branchRatio = 0.65;

        double cx = x + Math.cos(a) * branchRadius;
        double cy = y + Math.sin(a) * branchRadius;
        StdDraw.setPenRadius(0.001 * Math.pow(n, 1.2));
        StdDraw.line(x, y, cx, cy);
        if (n == 0) return;

        tree(n-1, cx, cy, a + bendAngle - branchAngle, branchRadius * branchRatio);
        tree(n-1, cx, cy, a + bendAngle + branchAngle, branchRadius * branchRatio);
        tree(n-1, cx, cy, a + bendAngle,               branchRadius * (1 - branchRatio));
    }

    public static void main(String[] args) {
        int n = Integer.parseInt(args[0]);
        StdDraw.enableDoubleBuffering();
        tree(n, 0.5, 0, Math.PI/2, 0.3);
        StdDraw.show();
    }
}