\begingroup
\small
\setlength{\tabcolsep}{4pt}
\begin{tabular}{rrrrrr}
\toprule
$J$ & $h$ & $L_h^2$ & $H_h^1$ & Time difference & Order\\
\midrule
32 & 0.25000 & $1.005\times10^{-2}$ & $1.421\times10^{-2}$ & $1.575\times10^{-2}$ & --\\
64 & 0.12500 & $2.612\times10^{-3}$ & $3.611\times10^{-3}$ & $4.003\times10^{-3}$ & 1.977\\
128 & 0.06250 & $6.492\times10^{-4}$ & $8.933\times10^{-4}$ & $1.001\times10^{-3}$ & 2.015\\
256 & 0.03125 & $1.577\times10^{-4}$ & $2.169\times10^{-4}$ & $2.433\times10^{-4}$ & 2.042\\
\bottomrule
\end{tabular}
\endgroup