you haven't defined the main() method correctly. You have

public static  void main  (String args)

it should be

public static void  main(String [] args)

I haven't tested your program, but looks ok otherwise

yeah, I just realised that after I had sent the msg.

Now the problem is I need the Top process to end so that the data
collected can be stored to the required output file. Hence, does
anyone know if it's possible to issues commands  like Control-C using
this approach. If so, how??

you can get a reference to the process like this

Process p = Runtime.getRuntime().exec("/usr/bin/top");

then read its output something like this

BufferedReader reader;
reader = new BufferedReader(new InputStreamReader(p.getInputStream()));

you could try using the getOutputStream() method to get an OutputStream you
could write your 'q' or control-c command to the 'top' process.

After much frustration I decided to call Process.getErrorSteam(),
which gives outputs:
stty: standard input: Invalid argument
top: tcgetattr() failed: Invalid argument

Does anyone know what the exact problem is here?? I've looked at the
man and info pages for stty, but haven't been able to pin point the
problem.