create push(Object obj) using stack?

if I want to create a NameList where it only hold names...
is there a good way to write the pushGirl(Object obj) and pushGuy(Object obj)?
here's how I want to use it...

PeopleList people = new PeopleList();
people.pushGuy( "John");
people.puthGirl ("Marry");

so, for example, do I write it like this?
public void pushGuy(Object obj) {
String name = new String( (String)obj ); // or String name = (String)obj; ??
// then what else should I do? thx...
}


Thx a thousand times...
Ben