Shell Programming and Scripting

HI all,
i want to run various Unix cmds thru a java prg. following is the code which i have written.
-------------------------------------------------------------------
import java.io.*;

class Run
{
public static void main(String[] args)
{
String ls_str;
try{
Process cmd_su = Runtime.getRuntime().exec("su - imail");
}
catch(Exception e){}
}
}
--------------------------------------------------------------------
the cmd su (switch users) works but i am not located there !!!!!!
any pointers will help me solving my problem ...

Thanks & Regards
SONAL

You may need to add the username to the wheel group to allow su to work with that username.