question: protected String url ( int zoomLevel , int xTile , int yTile ) { StringBuilder sb = new StringBuilder ( _url ) ; sb . append ( "/" ) ; sb . append ( zoomLevel ) ; sb . append ( "/" ) ; sb . append ( xTile ) ; sb . append ( "/" ) ; sb . append ( yTile ) ; sb . append ( ".png" ) ; return sb . toString ( ) ; }
target:  build a url request for a tile