public class RecursiveDemo {

   private static int depth;

   public static void main(String[] args) {
      depth = -1;
      if (args.length == 1) {
         int n = Integer.parseInt(args[0]);
         sumUpTo(n);
      }
      else {
         int m = Integer.parseInt(args[0]);
         int n = Integer.parseInt(args[1]);
         sumOfRange(m,n);
      }

      
   }

   /* Computes the sum of the integers in the range [0..n] using recursion.
   ** Also narrates its execution.
   */
   public static int sumUpTo(int n) {
      depth++; 
      printMessage("Received n:" + n);

      int result;
      if (n == 0) {
         result = 0;
      }
      else {
         int sumOfLesser = sumUpTo(n-1);
         printMessage("Adding n (" + n + ") to " + sumOfLesser);
         result = sumOfLesser + n;
      }
      printMessage(String.format("Having received %d; Returning %d",
                                 n, result));
      depth--;
      return result;
   }

   /* Computes the sum of the integers in the range [u..v] using recursion.
   ** Also narrates its execution.
   */
   public static int sumOfRange(int u, int v) {
      depth++; 
      printMessage(String.format("Received u:%d, v:%d", u, v));

      int result;
      if (u > v) {
         result = 0;
      }
      else {
         int sumFromVplus1 = sumOfRange(u+1, v);
         printMessage("Adding u (" + u + ") to " + sumFromVplus1);
         result = u + sumFromVplus1;
      }
      printMessage(String.format("Having received u:%d, v:%d; Returning %d",
                                 u, v, result));
      depth--;
      return result;
   }


   private static void printMessage(String s) {
      printSpaces(2*depth);
      System.out.println(s);
   }

   private static void printSpaces(int num) {
      for (int i=0; i != num; i++) { System.out.print(" "); }
   }

}