retrieving sub type from a <? extends Animal>

Question

There is an existing Set<Trump> that is passed on to another function that takes in a Set<? extends Politician> Set<? extends Politician> as an argument. Given that Set<? extends Politician> Set<? extends Politician> is going to contain either a Politician Object or a Trump Object only.

The Politican Class can't be modified. The Trump Class is available for modification.

Is there a way to cleanly do the following, or how should the derived class ( Trump ) be re-designed to be able to do this?

public Set<Trump> getSetOfTrump(Set<? extends Politician> politicianSet)
{
    //do some processing
    for(Politician pol : politicianSet){ //compiler is ok.. but I dont need Politician Object here
    }

    for(Trump t : politicianSet){ // any way to get Trump Objects out of politicianSet?
    }

} 

Answer 1

You'll have to filter the objects manually:

for(Politician t : politicianSet){ // any way to get Trump Objects out of politicianSet?
  if(t instanceof Trump) {
    //do your magic here
  }
}

The instanceof operator returns true if t is an instance of (a subclass of) Trump.

Answer 2

Below code would work -

public  Set<Trump> getSetOfTrump(Set<? extends Politician> politicians){
    return  politicians.stream().filter( s  -> s instanceof Trump).map(s ->(Trump)s).collect(Collectors.toSet());
}