code: void reset(Object[] copyFrom, Object upperBound, UpdateFunction updateFunction, Comparator comparator)
      {
          this.copyFrom = copyFrom;
          this.upperBound = upperBound;
          this.updateFunction = updateFunction;
          this.comparator = comparator;
          maxBuildKeyPosition = Math.max(maxBuildKeyPosition, buildKeyPosition);
          buildKeyPosition = 0;
          buildChildPosition = 0;
          copyFromKeyPosition = 0;
          copyFromChildPosition = 0;
      }
docs: reset counters/setup to copy from provided node