observables represents the sources of data where as observers (subscribers) listen to them. in nutshell, an observable emits items and a subscriber then consumes these items.

observable

• observable provides data once subscriber starts listening.

• observable can emit any number of items.

• observable can emit only signal of completion as well with no item.

• observable can terminate successfully.

• observable may never terminate. e.g. a button can be clicked any number of times.

• observable may throw error at any point of time.

subscriber

• observable can have multiple subscribers.

• when an observable emits an item, each subscriber onnext() method gets invoked.

• when an observable finished emitting items, each subscriber oncomplete() method gets invoked.

• if an observable emits error, each subscriber onerror() method gets invoked.