@FunctionalInterface
public interface A {

List<ItemB> a1(ItemA itemA);
}


@FunctionalInterface
public interface B {

List<ItemA> b1(ItemB itemB);
}

class MyClass{
public <T,R> boolean execute(ItemA itemA, Function<T,R> function){
 function = ItemA.a1();
//**how can I pick either ItemA or ItemB interface method and define it here?**
}
}