code: public static void setFaceNames(String[] nameArray)
      {
          if (nameArray.length != 6)
          {
              throw new IllegalArgumentException("nameArray length is not 6.");
          }
          for (int i = 0; i < 6; i++)
          {
              faceIndexMap.put(nameArray[i], i);
          }
      }
docs: Set the names of six images in the zip file. The default names of the six
  images are "posx.png", "negx.png", "posy.png", "negx.png", "posz.png",
  and "negz.png". If the names of the six images in the zip file are
  different to the default ones, this function must be called before load
  the zip file.
  
  @param nameArray
  An array containing six strings which are names of images
  corresponding to +x, -x, +y, -y, +z, and -z faces of the cube
  map texture respectively.