/* Java class containing several recursive methods that "narrate" their own
** execution, for the purpose of aiding the understanding of how recursion
** works.
*/
public class RecursionExamples {

   private static final int DEPTH_INDENT = 3;

   private static int depth;


   /* Returns the sum of the integers in the range [low..high].
   */
   public static int sumOfRange(int low, int high) {
      int result = 0;
      depth = depth + 1;
      println(depth, "Received low: " + low + "; high: " + high); 
      if (low > high) {
         result = 0;
      }
      else {
         result = low + sumOfRange(low+1, high);
      }
      println(depth, "Returning " + result + ", having received " +
              low + "; high: " + high);
      depth = depth - 1;
      return result;
   }


   public static void main(String[] args) {
      depth = -1;
      sumOfRange(4,8);
   }


   // methods for printing messages that appear after an appropriate
   // indent in accord to the recursive depth of the calling instance.
   // ----------------------------------------------------------------

   /* Prints the given string (s) following an indent indicated by 'depth'.
   */
   private static void print(int depth, String s) {
      int indent = DEPTH_INDENT * depth;
      printSpaces(indent);
      //String format = "%" + indent + "s%s";
      System.out.print(s);
   }

   /* Prints the given string (s) following an indent indicated by 'depth';
   ** then skips to the next line.
   */
   private static void println(int depth, String s) {
      print(depth, s);
      System.out.println();
   }

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