Question

Often I find the need to engineer objects with configurable functionality.

To exemplify, assume I’m creating a DateIterator. The configurable option(s) might be whether to iterate the closed interval [start, end] or the open-end interval [start, end).

---

• (1) The, in my opinion, ungraceful solution – limited to only one true/false configuration option

new DateIterator(boolean openInterval);

• (2) The typesafe enum way – typically a bit bulky

new DateIterator(Interval.OPEN_END);

• (3) The unconventional attempt – nice but not too straight forward

new DateIterator().openEnd();

• (4) The inheritance approach – often over-engineering

new OpenEndedDateIterator();

---

To this comes a few alternatives which I consider inferior, like integer-based configuration new DateIterator(Interval.OPEN_END); or property based configuration.

Are there any other approaches? Which approach you do you prefer?

Answer 1

I’d say the Builder pattern makes sense here:

DateIterator di = 
  DateIterator.builder()
              .withStartDate(new Date())
              .withOpenEnd()
              .build();

That way your actual DateIterator can be immutable, while the builder returned by DateIterator.builder() does the configuration work.