Why i cannot compile?

Question

The error message is:
unreported exception son; must be caught or declared to be thrown
The code:
class father extends Exception{
     public String toString()
          return "father";
class son extends father
     public String toString()
          return "son";
public class ExceptionTest
     public void f() throws father{}
     public void s() throws son{}
     public static void main(String arg[])
          ExceptionTest et=new ExceptionTest();
          try{
          //et.f();
          et.s();
     }catch(son s)
          s.printStackTrace();
          throw s; //here have a mistake?
     catch(father f)
          f.printStackTrace();
          

Answer 1

There may be several catch-blocks after try-block - in order to catch different classes of exceptions. But they catch only exceptions thrown in try-block
how can the code get work?variant 1:
public static void main(String arg[]) throws s
variant 2:
public static void main(String arg[]){
  ExceptionTest et=new ExceptionTest();
  try {
    try{
     et.s();
    catch(son s) {
      s.printStackTrace();
      throw s;
  catch(father f) {
    f.printStackTrace();
}