\documentclass[10pt]{article}
\usepackage{xepersian}
\settextfont{XB Niloofar}
\newsavebox\myboxxx

\newcommand{\Class}[1]
{ 
\sbox{\myboxxx}{\texttt{#1}}
\fbox{\parbox{\wd\myboxxx}{#1}}
}


\begin{document}

\Class
{double Width\\
 double Height\\
 double Perimeter\\ 
 double Area\\
}


\usebox\myboxxx


\end{document}