why do i get an exception?

[Damien Howard]

 
        String clearScreenCommand = null;
if( System.getProperty( "os.name" ).startsWith( "Window" )){
    clearScreenCommand = "cls";
    System.out.println("in win"+System.getProperty("os.name"));
}else if(System.getProperty( "os.name" ).startsWith( "Linux" )){
    clearScreenCommand = "clear";
}else{}
try{
    Runtime.getRuntime().exec(clearScreenCommand);
}catch(IOException e){
    System.out.println("exception in clear"+clearScreenCommand);
    e.printStackTrace();
}
 

I am running this on a windows machine. It goes into the windows clause and it assigns cls to my var, but I get an IOException and my cmd window is not cleared. Does anyone know why?

[Ernest Friedman-Hill]

Probably because here's no "cls.exe"; it's a command built into the shell. You'd have to exec something like "cmd /E cls" -- i.e., run the shell, and tell it to execute the cls command.

But -- and this is a big "but" -- that shell wouldn't be connected to a terminal window; it takes input from the Java process. So the cls command would have no effect!

There are two ways to clear a terminal window from a Java program: first, send a (platform dependent) escape sequence to the terminal to clear it (Google for "ANSI escape codes" to learn more) or just print a bunch of blank lines to make the contents of the screen scroll away!

[Steve Morrow]

Navigate yourself around pitfalls related to the Runtime.exec() method