private boolean checkDiagonalUp(int x, int y){
		// Find the minimum and maximum x and y values which have the same mark
		int minX = x;
		int minY = y;
		while (minX > 0 && minY > 0 && boardCells[minX - 1][minY - 1].equals(boardCells[x][y])) {
			minX--;
			minY--;
		}
		int maxX = x;
		int maxY = y;
		while ((maxX + 1) < boardCells.length && (maxY + 1) < boardCells.length &&
				boardCells[maxX + 1][maxY + 1].equals(boardCells[x][y])) {
			maxX++;
			maxY++;
		}
		// If the difference is larger than 4, we have 5 in a row
		// We only have to check X (or Y) as the difference is the same for both
		return maxX - minX >= 4;
	}