I can't fullfill the requestst - when I try this:
private void restart()  {
 isGameStopped = false;
        countClosedTiles = SIDE * SIDE;
        score = 0;
        countMinesOnField = 0;
I got following error: The createGame() method must clear all items (flags, mines, numbers) from the playing field. Use the setCellValue(int, int, String) method. Pass an empty string as the last argument. When I try to add to the code following piece:
for (int y=0; y<SIDE; y++)  {
            for (int x=0; x<SIDE; x++)  {
                setCellValue(x, y, "");
I got a lot of weird errors, for instance, that I have to assign false to isGameStopped field. But I am do doing this! My game works correctly, but I can't pass the tests. :-(