How to avoid calling implements at 2 activites?

Question

I have two activities: MainActivity extends ListActivity and Preferences implements BillingController.IConfiguration .

Now I need to call BillingController.someMethod(this) at MainActivity . Such call can be made only if MainActivity implements BillingController.IConfiguration . But this is already implemented at Preferences class. What can I do to avoid implementing that again?

Answer 1

Make a class that implements BillingController.IConfiguration and use it inside both MainActivity and Preferences to delegate method calls to it.

Answer 2

Do an instance of check.

if (instance instanceof BillingController.IConfiguration) {
    ((BillingController.IConfiguration)instance).someMethod(this);
}