val source: PublishSubject<Int> = PublishSubject.create()
// subscribe with FirstObserver
source.subscribe { number -> Log.d("PublishSubject", "FirstObserver onNext: $number") }
source.onNext(1)
source.onNext(2)
source.onNext(3)
// subscribe with SecondObserver
source.subscribe{ number -> Log.d("PublishSubject", "SecondObserver onNext: $number") }
source.onNext(4)
source.onComplete()

// OUTPUT:
FirstObserver onNext: 1
FirstObserver onNext: 2
FirstObserver onNext: 3
FirstObserver onNext: 4
SecondObserver onNext: 4