Dragon.java

Below is the syntax highlighted version of Dragon.java from §3.2 Creating Data Types.

/*************************************************************************
 *  Compilation:  javac Dragon.java
 *  Execution:    java Dragon N
 * 
 *  Draws dragon curve of order N.
 *
 *  % java Dragon 7
 *
 *  Limitations
 *  -------------
 *    -  N must be between 1 and 15
 *
 *************************************************************************/


public class Dragon {
    private Turtle turtle;

    public Dragon(int N) {
     /**************************************************************************
      *  The following constants are used to figure out where to start         
      *  drawing the dragon curve.  left[i] = maximum number of steps taken
      *  to the left in dragon(i).  right[i], up[i], down[i] are similar.
      **************************************************************************/
      int[] left  = { 0, 0, 0, 2, 4, 5, 5,  5,  5,  5, 10, 42, 74, 81,  85,  85 };
      int[] right = { 1, 1, 1, 1, 1, 1, 2, 10, 18, 21, 21, 21, 21, 21,  57, 170 };
      int[] up    = { 0, 1, 2, 2, 2, 2, 2,  2,  5, 21, 37, 42, 42, 42,  42,  42 };
      int[] down  = { 0, 0, 0, 0, 1, 5, 9, 10, 10, 10, 10, 10, 23, 85, 149, 165 };


      double size = Math.max(left[N] + right[N], up[N] + down[N]);
      double x = (right[N] - left[N]) / 2.0;
      double y = (up[N]    - down[N]) / 2.0;

      turtle = new Turtle(0.0, 0.0, 0.0);
      turtle.setXscale(x - size/2, x + size/2);
      turtle.setYscale(y - size/2, y + size/2);
      dragon(N);
    }


   // dragon curve of order n
   public void dragon(int n) {
      if (n == 0) {
         turtle.goForward(1.0);
      }

      else {
         dragon(n-1);
         turtle.turnLeft(90);
         nogard(n-1);
      }
   }
   
   // reverse dragon curve of order n
   public void nogard(int n) {
      if (n == 0) {
         turtle.goForward(1.0);
      }
      else {
         dragon(n-1);
         turtle.turnLeft(-90);
         nogard(n-1);
      }
   }



   public static void main(String[] args) {
      int N = Integer.parseInt(args[0]);
      if (N < 0 || N > 15) {
         System.out.println("Try a number between 1 and 15 next time.");
         System.exit(0);
      }

      new Dragon(N);


   }
}