trouble with execute an command at apache exec in java -

i want run file (a.txt) using apache commons exec libraries . gives me error : problem?

exception in thread "main" java.io.ioexception: cannot run program "a.txt" (in directory "c:\users\sinaa\desktop"): createprocess error=2, system cannot find file specified

my code :

    public static void main(string[] args) throws ioexception {      executor exec = new defaultexecutor();     file temp=new file("c:\\users\\sinaa\\desktop");     exec.setworkingdirectory(temp);     commandline s=new commandline("a.txt");     exec.execute(s); } 

from comment:

i want open a.txt in notepad window when compile code

to open file in java using default associated application, use desktop class:

try{     desktop.open("a.txt"); }catch(ioexception io){     io.printstacktrace(); }