Changing code in listings dynamically

Question

I need to change dynamically the code in the listing by adding just one key word to the code. I tried to do it like this:

\begin{lstlisting}[escapechar=|]
  class MyThread extends Thread {
  private |\only<3>{\alert{volatile}}| boolean stop = false;

  public void run() {
    while (!stop) {
        doSomeWork();
    }
  }
  public void setStop() {
    this.stop = true;
  }
}
\end{lstlisting}

It works ok, but there are two spaces between "private" and "boolean" when the "volatile" is not visible. Is there any other way to make what I want?

Answer 1

If you don't mind me changing your implementation slightly, here is my solution. Put your code in a separate file and then bring it in like the following example. By doing so, first you avoid any kind of unexpected behaviors like the one you are having now, and second, you can easily and simply add as many keywords as you want:

\documentclass{article}
\usepackage{listings}
\usepackage{xcolor}


\begin{document}
\lstset{
        language=Java,
        tabsize=3,
        %frame=lines,
        caption=A test file,
        label=code:test,
        frame=shadowbox, 
        rulesepcolor=\color{gray},
        xleftmargin=20pt,
        framexleftmargin=15pt,
        keywordstyle=\color{blue}\bf,
        commentstyle=\color{OliveGreen},
        stringstyle=\color{red},
        numbers=left,
        numberstyle=\tiny,
        numbersep=5pt,
        breaklines=true,
        showstringspaces=false,
        basicstyle=\footnotesize,
        %add your keywords here:
        emph={volatile},emphstyle={\color{magenta}}}
        %load the file here:
        \lstinputlisting{test.java}

\end{document}

The keywords are added in the last line of lstset (emph={volatile}). You can add more by separating them with ,