Code Snippet IN Text

Since LaTeX is meant primarily intended for printed text I would strongly recommend you to not use e.g. grey background, but just use a typewriter font, e.g.

The class \texttt{List.class} is \ldots

You can and should wrap this in a new command to be free to change the visual appearance later, e.g.

\newcommand{\code}[1]{\texttt{#1}}

so you can use a form which is free of formating distractions and conveys intention more clearly

The class \code{List.class} is \ldots

If, however, you are intent upon marking the text with a gray background, you can extend the above format with a color definition and colorbox from the colors or xcolors package, e.g.

\definecolor{codegray}{gray}{0.9}
\newcommand{\code}[1]{\colorbox{codegray}{\texttt{#1}}}

For more on the colors, see this tutorial for some other usage examples.

The listings package has a command \lstinline{snippet} that is used exactly for that. You can configure its appearance (including syntax highlighting) using the package options.