How to implement code signing in Jini,rmi and applets

First paragraph code: generate a public/private key pair and specify the file on the command line to write the key pair to the file.

Import java.security.*
Import java.io.*
public class Keypairgen
{
public static void main (Stri Ng[] args
{
if (args.length!=1)
{
System.out.println (Usage:java keypairgen keyfile);
System.exit (1);
}
Keypairgen obj=new Keypairgen ();
try{
Obj.gen (args[0]);
} catch (NoSuchAlgorithmException ex)
{
System.out.println ("nosuchalgorithmexception");
}
catch (FileNotFoundException ex)
{
System.out.println ("FileNotFoundException");
}
catch (IOException ex)
{
System.out.println ("IOException");
}
}
public void Gen (String source) throws NoSuchAlgorithmException,
Filenotfoundexception,ioexception
{ br> keypairgenerator kpgen=keypairgenerator.getinstance ("DSA");
Kpgen.initialize (512);
KeyPair Kpair=kpgen.genkeypair ();
FileOutputStream fos=new FileOutputStream (source);
ObjectOutputStream oos=new objectoutputstream (FOS);
Oos.writeobject (Kpair);
Fos.close ();br> Oos.close ();
}
}