\documentclass[a4paper,12pt]{article}
\usepackage{amssymb} % needed for math
\usepackage{amsmath} % needed for math
\usepackage[utf8]{inputenc} % this is needed for german umlauts
\usepackage[ngerman]{babel} % this is needed for german umlauts
\usepackage[T1]{fontenc}    % this is needed for correct output of umlauts in pdf
\usepackage[margin=2cm]{geometry} %layout
\usepackage{minted} % needed for the inclusion of source code

\begin{document}
\renewcommand{\theFancyVerbLine}{
  \sffamily\textcolor[rgb]{0.5,0.5,0.5}{\scriptsize\arabic{FancyVerbLine}}}
\inputminted[linenos,
               numbersep=7pt,
               gobble=0,
               frame=lines,
               framesep=2mm,
				label=AbstractClass.java,
				fontsize=\footnotesize, tabsize=4]{java}{AbstractClass.java}
\clearpage
\inputminted[linenos,
               numbersep=7pt,
               gobble=0,
               frame=lines,
               framesep=2mm,
				label=ConcreteClass.java,
				fontsize=\footnotesize, tabsize=4]{java}{ConcreteClass.java}

\end{document}