instanceof keyword usage

Question

Is using the instanceof keyword against the essence of object oriented programming? I mean is it a bad programming practice? I read somewhere that us

Answer 1

Another usage of instaceOf operation could be error handling. If you have similar error handling for exceptions, and you want to have it all in one place you can use:

public void handleError(Throwable t, HttpServletRequest req) {
   if (t instaceOf ValidationException) {
              ...doSomewthing......
   } else    if (t instaceOf DataException) {
              ...doSomewthing......
   } else    if (t instaceOf DataException) {
              ...doSomewthing......
   } else {
              ...doSomewthing......
   }

}

with above code, you avoid to have many

} catch  {

blocks and instead have just one

} catch (Throwable t) {
   handleError(t, request);
   return "errorPage" or whateveryouwant;
}

Also, one more thing is, is you check java source code, you will find so many usages of instaceof..

And one good link: article about usage of instaceof