GWT: Timer and Scheduler Classes

Question

I have read this page over several times, and am just not seeing some of the inherent differences between GWT\'s Timer and Scheduler classes. I\'m

Answer 1

As the JavaDoc says, DeferredCommand is deprecated in favor of Scheduler. The problem with DeferredCommand and IncrementalCommand is that they have a static state (which makes it hard to use reliably in tests). Moreover, their (static) methods make JSNI calls which forces you to use a GWTTestCase to test your code (static methods aren't –easily– mockable). Static methods also make it impossible to wrap them (to, e.g. add some logging or whatever).
On the other hand, you work with an instance of a Scheduler (if you want testable code, you'll use dependency-injection to get a instance of a scheduler and will never call Scheduler.get() except in your DI "factory"). In a test, you can then use a StubScheduler for instance.

Then there's Timer, which is similar to the others but the scheduled task can be cancelled. Note that Timer makes use of JSNI too, just like DeferredCommand; any kind of code that uses a Timer will need a GWTTestCase to be unit-tested.