if (axis == X_AXIS) return spansX[childIndex]; else return spansY[childIndex];
if (axis != X_AXIS && axis != Y_AXIS) throw new IllegalArgumentException("Illegal axis argument"); return spans[axis][childIndex];
  protected int getSpan(int axis, int childIndex)  {    if (axis == X_AXIS)      return spansX[childIndex];    else      return spansY[childIndex];  }