[Tex/LaTex] How to get “Appendix” and on same line

Question

Is it possible to get "Appendix X" and on the same line, maybe with a colon after the appendix identifier letter?

MWE:

\documentclass{report} 
\begin{document}
\tableofcontents
\chapter{CHapter one name}
\chapter{Chapter two name two}
\appendix
\chapter{Theory}
\section{Some theory}
\section{Some other theory}
\chapter{Method}
\section{LOLZ}
\section{ROLF}
\end{document}

As you can see, the compiled PDF writes:

Appendix A

Theory

A.1 Some Theory

I want it to be something like this:

Appendix A: Theory

A.1 Some Theory

Answer 1

Here is a way, with titlesec and apptools. Appendix chapters are placed at to the top of the page, but the spacing parameters can be changed at will:

\documentclass{report}

\usepackage{showframe} 
\usepackage{titlesec}
\usepackage{apptools}
\AtAppendix{\titleformat{\chapter}[block]{\LARGE\bfseries}{\appendixname~\thechapter:}{0.333em}{}%
\titlespacing*{\chapter}{0pt}{-20pt}{40pt}}

\begin{document}

\tableofcontents
\chapter{Chapter one name}
\chapter{Chapter two name two}

\appendix
\chapter{Theory}
\section{Some theory}
\section{Some other theory}
\chapter{Method}
\section{LOLZ}
\section{ROLF}

\end{document}