private boolean calculateGameOver(){
		for(int x = 1; x <= FIELD_SIZE; ++x){
			for(int y = 1; y <= FIELD_SIZE; ++y){
				if(field[x][y] <= 0){ return false; }
				else if(
					field[x-1][y] == field[x][y] ||
				    field[x+1][y] == field[x][y] ||
				    field[x][y-1] == field[x][y] ||
				    field[x][y+1] == field[x][y]
				){
					return false;
				}
			}
		}
		return true;
	}