Where should the code go; in Fragment or in Activity?

Where should the code go; in Fragment or in Activity?

Imagine this situation:
Activity.
Activity contains layout with 2 fragments. FragmentA and FragmentB
FragmentA has a layout with a button that should print a toast "Hello".
FragmentB has a layout with a button that should print a toast "Bye".
Both buttons have a onClick attribute set. First one with "sayHello" and
second one with "SayBye".
So which is the correct way of finally displaying the toast?
Case A:
public class ActivityCustom extends FragmentActivity{
[...]
public void sayHello(View v){
//SHOW TOAST HERE
}
public void sayBye(View v){
//SHOW TOAST HERE
}
}
Case B:
public class ActivityCustom extends FragmentActivity{
[...]
public void sayHello(View v){
((FragmentA)this.findFragmentById(R.id.fragmentA)).showToast();
}
public void sayBye(View v){
((FragmentB)this.findFragmentById(R.id.fragmentB)).showToast();
}
}
I'm a bit confused about that.
Because if we delegate all the work on the fragments, I guess Activity
will be kinda clear of code. It will just have the code to "connect" the
two fragments, right?