code: protected String fillPlaceHolders(String url, int x, int y, int z) {
  		url = url.replace("{x}", Integer.toString(x));
  		url = url.replace("{y}", Integer.toString(y));
  		url = url.replace("{-y}", Integer.toString(y));
  		return url.replace("{z}", Integer.toString(z));
  	}
docs: Fill in the {x}, {y} and {z} placeholders in the URL.
  
  @param url The URL with placeholders.
  @param x   The x-coordinate to the tile.
  @param y   The y-coordinate to the tile.
  @param z   The tile level.
  @return The URL with filled placeholders.