Design Pattern – RxJava 2 & Reactive programming

What is it?

Real world

Think of it as a network of water pipes.

• You have a source, our water tank
• Then a series of pipes and connectors
  • which may divert flows to various rooms
  • or change the water into something else

Participants

• An Observable (water tank) emits items
• An optional Transformation (water connector?) transforms items into
• A consumer is a doer which can act on those items
• A Subscriber consumes those items
  • Observables don’t start emitting items until someone explicitly subscribes to them

Coding example

// We want to print the words in UPPERCASE

// Observable
Observable<String> observable = Observable.just("how", "to", "do", "in", "java");

// Consumer
Consumer<? super String> consumer = System.out::println;
 
observable
    // Transformation using map() method
    .map(w -> w.toUpperCase())
    
    // Subscriber
    .subscribe(consumer);

Communication flow

• Connect the subscriber to consumer using subscribe()
• As soon as, we connect both,
  • events start flowing
  • subscriber start act on events by consumer
• Internally, when event is emitted from the observable,
  • the onNext() method is called on each subscriber
  • onComplete() or the onError() method is called on the subscriber when the observable finishes all of events