code: public boolean isNotVisited(int loc) {
      if (checkBounds(loc)) {
        return (ZERO == this.registry[loc]);
      }
      else {
        throw new RuntimeException(
            "The location " + loc + " out of bounds [0," + (this.registry.length - 1) + "]");
      }
    }
docs: Check if position is not visited.
  
  @param loc The index.
  @return true if not visited.