\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{listings}

\begin{document}

\clearpage

\begin{tabular}{|l|l|}

\begin{lstlisting}[basicstyle={\scriptsize\ttfamily},
identifierstyle={\color{black}},
tabsize=2,language={[AspectJ]Java},
numbersep=8pt,numbers=left,xleftmargin=0.5cm,frame=tlbr,framesep=2pt,framerule=0pt,
morekeywords={class,run}]

class PrintHelloThread ext Thread {
    void run(Dummy x) {
        out.println("Hello world")
    }
}
class X ext ProxifiedObject {
    PrintHelloThread thread
    void main(X x) {
        x.thread := new PrintHelloThread;
        x.thread.start(0);
        x.thread.join(0);
    }
}
\end{lstlisting}
&
\begin{lstlisting}[
basicstyle={\scriptsize\ttfamily},
identifierstyle={\color{black}},
tabsize=2,
language={[AspectJ]Java},
numbersep=8pt,
numbers=left,
xleftmargin=0.5cm,frame=tlbr,framesep=2pt,framerule=0pt,
morekeywords ={class,run}
]
class PrintHelloThread ext Thread {
    void run(Dummy x) {
        out.println("Hello world")
    }
}
class X ext ProxifiedObject {
    PrintHelloThread thread
    void main(X x) {
        x.thread := new PrintHelloThread;
        x.thread.start(0);
        x.thread.join(0);
    }
}
\\
\end{lstlisting}
\end{tabular}
\end{document}