code: public static TileCache createExternalStorageTileCache(Context c,
                                                             String id, int firstLevelSize, int tileSize, boolean persistent) {
          return createExternalStorageTileCache(c.getExternalCacheDir(), id, firstLevelSize, tileSize, persistent);
      }
docs: Utility function to create a two-level tile cache along with its backends.
  
  @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
  @param persistent     whether the second level tile cache should be persistent
  @return a new cache created on the external storage