code: public static TileCache createExternalStorageTileCache(Context c, String id, int firstLevelSize, int tileSize) {
          return createExternalStorageTileCache(c, id, firstLevelSize, tileSize, false);
      }
docs: Utility function to create a two-level tile cache along with its backends.
  This is the compatibility version that by default creates a non-persistent cache.
  
  @param c              the Android context
  @param id             name for the directory, which will be created as a subdirectory of the default cache directory (as
  returned by {@link android.content.Context#getExternalCacheDir()}).
  @param firstLevelSize size of the first level cache (tiles number)
  @param tileSize       tile size
  @return a new cache created on the external storage