java generics - returning subtype announced form method

my category implementing super-class slight which advantage list<jcomponent>. list being returned read-only:

public summary category superclass {
    open summary list<jcomponent> getcomponents();
}

in class, i wish relapse domain announced list - i.e. sub-list:

public category subclass extends superclass {
    private list<jbutton> buttons;
    open list<jcomponent> getcomponents() {
        relapse buttons;
    }
}

this generates compiler error, list<jbutton> subtype list<jcomponent>.

i know since doesn't compile, shouldn't certified supplement jtextfield list jbuttons.

however, list read-only, following "conceptually" should allowed. but, course, compiler doesn't know read-only.

is there any proceed grasp i wish achieve, but changing slight chapter super-class, domain chapter sub-class?

thanks,
calum