So you have heard about RxJava, maybe checked out some articles, videos or even code - but things are still not that clear!? The aim of this talk is first of all to create the reactive programming mindset; to explain what an Observable and a Subscriber are; and to give a bit of insight in the magic of thread handling in RxJava. We will then take a practical example, see how RxJava can be applied and what its advantages are compared to other options. I will end the talk by addressing an important question: how to best proceed to integrate RxJava into an existing app.

1. 11
The ABCs of
RxJava
Florina Muntenescu
@FMuntenescu

2. 22
The ABCs of
RxJava
Making a Burger
Florina Muntenescu
@FMuntenescu

3. 3
Donald Duck’s
Burger Joint

4. 4
Huey Dewey Louie

5. 5
Huey

6. 6
Dewey

7. 7
Louie

8. 8
Huey
Dewey
Louie

9. 9
filter(meat -> isMeatFresh(meat))
map(meat -> cook(meat))
Dewey

10. 10
zip

11. 11
zip

12. 12
zip

13. 13
zip

14. 14
STREAMS OF DATA

15. 15
STREAMS OF DATA

16. 16
STREAMS OF DATA

17. 17
zip
STREAMS OF DATA

18. 18
Consumer
Observable
Subscriber

19. 19
filter(meat -> isMeatFresh(meat))
map(meat -> cook(meat))
operators

20. 20
Huey.getBun()

21. 21
filter(meat -> isMeatFresh(meat))
for(Meat meat: meatList){
if(!isMeatFresh(meat)){
meatList.remove(meat);
}
}

22. 22
Observable.from(meatSource)
.filter(meat ->
isMeatFresh(meat))
filter(meat -> isMeatFresh(meat))

23. 23
filter(meat -> isMeatFresh(meat))
map(meat -> cook(meat))
for(Meat meat: meatList){
meat = cook(meat);
}

24. 24
Observable.from(meatSource)
.filter(meat ->
isMeatGoneBad(meat))
.map(meat -> cook(meat));
filter(meat -> isMeatFresh(meat))
map(meat -> cook(meat))

25. 25
Observable<Burger> burgerObservable =
Observable.zip(bunObservable,
meatObservable,
tomatoObservable,
(bun, meat, tomato) ->
makeBurger(bun, meat, tomato))
bunObservable
meatObservable
tomatoObservable
burgerObservable

26. 26
Observable<Burger> burgerObservable =
Observable.zip(bunObservable,
meatObservable,
tomatoObservable,
(bun, meat, tomato) ->
makeBurger(bun, meat, tomato))
bunObservable
meatObservable
tomatoObservable
burgerObservable

27. 27
Consumer
Observable
Subscriber
.subscribe

28. 28
Subscriber
burgerObservable
.subscribe(mickeySubscriber);

29. 29
Subscriber
onNext(Burger burger)
onCompleted()
burgerObservable
.subscribe(
burger -> eatBurger(burger),
error -> complain(error),
() -> leaveBurgerJoint());
// onNext
//onError
//onCompleted
onError(Throwable error)

30. 30
Observable.zip(bunObservable,
meatObservable,
tomatoObservable,
(bun, meat, tomato) ->
makeBurger(bun, meat, tomato))
.subscribe(burger -> eatBurger(burger),
error -> complain(error)); // dining area
// dining area

31. 31
// kitchen
// dining area
Observable.zip(bunObservable,
meatObservable,
tomatoObservable,
(bun, meat, tomato) ->
makeBurger(bun, meat, tomato))
.subscribe(burger -> eatBurger(burger),
error -> complain(error));

32. 32
// kitchen
// dining area
Observable.zip(bunObservable,
meatObservable,
tomatoObservable,
(bun, meat, tomato) ->
makeBurger(bun, meat, tomato))
.subscribeOn(kitchen)
.observeOn(dining area)
.subscribe(burger -> eatBurger(burger),
error -> complain(error));

33. 33
Observable.zip(bunObservable,
meatObservable,
tomatoObservable,
(bun, meat, tomato) ->
makeBurger(bun, meat, tomato))
.subscribeOn(Schedulers.computation())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(burger -> eatBurger(burger),
error -> complain(error));// dining area
// kitchen

34. 34
Stream of data
Observable
Subscriber
Operators
Threads

35. 35
Creating Observables

36. 36
Creating Observables
From a List

37. 37
List<Burger> burgers = new ArrayList<>();
burgers.add(new Burger());
burgers.add(new Burger());
Observable<Burger> burgerObservable =
Observable.from(burgers);

38. 38
List<Burger> burgers = new ArrayList<>();
burgers.add(new Burger());
burgers.add(new Burger());
Observable<Burger> burgerObservable =
Observable.from(burgers);
1 2

39. 39
Observable<Burger> burgerObservable =
Observable.from(burgers);
burgerObservable.subscribe(new Subscriber<Burger>() {
@Override
public void onNext(final Burger burger) {
}
@Override
public void onCompleted() {
}
@Override
public void onError(final Throwable e) {
}
});

40. 40
Observable<Burger> burgerObservable = Observable.from(burgers);
burgerObservable.subscribe(new Subscriber<Burger>() {
@Override
public void onNext(final Burger burger) {
// handle burger 1
}
@Override
public void onCompleted() {
}
@Override
public void onError(final Throwable e) {
}
});
1

41. 41
Observable<Burger> burgerObservable = Observable.from(burgers);
burgerObservable.subscribe(new Subscriber<Burger>() {
@Override
public void onNext(final Burger burger) {
// handle burger 2
}
@Override
public void onCompleted() {
}
@Override
public void onError(final Throwable e) {
}
});
1 2

42. 42
Observable<Burger> burgerObservable = Observable.from(burgers);
burgerObservable.subscribe(new Subscriber<Burger>() {
@Override
public void onNext(final Burger burger) {
}
@Override
public void onCompleted() {
// no more burgers!
}
@Override
public void onError(final Throwable e) {
}
});
1 2

43. 43
Observable<List<Burger>>
List<Burger> burgers = new ArrayList<>();
burgers.add(new Burger());
burgers.add(new Burger());
burgerObservable =
Observable.just(burgers);

44. 44
1
Observable<List<Burger>>
burgerObservable =
Observable.just(burgers);
List<Burger> burgers = new ArrayList<>();
burgers.add(new Burger());
burgers.add(new Burger());

45. 45
Observable<List<Burger>> burgerObservable =
Observable.just(burgers);
burgerObservable.subscribe(
new Subscriber<List<Burger>>() {
@Override
public void onNext(final List<Burger> burgers) {
}
@Override
public void onCompleted() {
}
@Override
public void onError(final Throwable e) {
}
});

46. 46
Observable<List<Burger>> burgerObservable =
Observable.just(burgers);
burgerObservable.subscribe(
new Subscriber<List<Burger>>() {
@Override
public void onNext(
final List<Burger> burgers) {
// handle the list of burgers
}
@Override
public void onCompleted() {
}
@Override
public void onError(final Throwable e) {
}
});
1

47. 47
Observable<List<Burger>> burgerObservable =
Observable.just(burgers);
burgerObservable.subscribe(
new Subscriber<List<Burger>>() {
@Override
public void onNext(
final List<Burger> burgers) {
// handle the list of burgers
}
@Override
public void onCompleted() {
// no more burgers!
}
@Override
public void onError(final Throwable e) {
}
});
1

48. 48
Creating Observables
From
Click Events

49. 49

50. 50

51. 51

52. 52
[click!] [click!] [click!]

53. 53
???.subscribe(new Subscriber<String>() {
@Override
public void onNext(final String s) {
// called on every click
}
@Override
public void onCompleted() {
}
@Override
public void onError(final Throwable e) {
}
});

54. 54
[click!] [click!] [click!]
???.onNext(…) ???.onNext(…) ???.onNext(…)

55. 55
burgerButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(final View view) {
}
});
PublishSubject<String> burgerRequestedSubject =
PublishSubject.create();

56. 56
burgerButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(final View view) {
burgerRequestedSubject.onNext(…);
}
});
PublishSubject<String> burgerRequestedSubject =
PublishSubject.create();

57. 57
burgerRequestedSubject.subscribe(new Subscriber<String>() {
@Override
public void onNext(final String s) {
// called on every click
}
@Override
public void onCompleted() {
// will never be called for click events
}
@Override
public void onError(final Throwable e) {
}
});

58. 58
Creating Observables
From
Declarative
Code

59. 59
public Burger cook(){
// cooking is time consuming
return burger;
}
Observable<Burger> burgerObservable =
Observable.fromCallable(this::cook);

60. 60
Error
Handling

61. 61
Thread t = new Thread(new Runnable() {
@Override
public void run() {
cook();
}
});

62. 62
Thread t = new Thread(new Runnable() {
@Override
public void run() {
try{
cook();
} catch(Exception e) {
// handle exception
}
}
});

63. 63
getMeatObservable()
.filter(meat -> isMeatFresh(meat))
.map(meat -> cook(meat))
.subscribeOn(
meat -> doSomething(),
error -> complain(error));

64. 64
getMeatObservable()
.filter(meat -> isMeatFresh(meat))
.map(meat -> cook(meat))
.subscribeOn(
meat -> doSomething(),
error -> complain(error));

65. 65
public Observable<Meat> getCookedMeat() {
return getMeatObservable()
.filter(meat -> isMeatFresh(meat))
.map(meat -> cook(meat));
}
Observable.zip(getBun(),
getCookedMeat(),
getTomatoSlice(),
(bun, meat, tomato) ->
makeBurger(bun, meat, tomato))
.subscribeOn(
burger -> eatBurger(burger),
error -> complain(error));

66. 66
public Observable<Meat> getCookedMeat() {
return getMeatObservable()
.filter(meat -> isMeatFresh(meat))
.map(meat -> cook(meat));
}
Observable.zip(getBun(),
getCookedMeat(),
getTomatoSlice(),
(bun, meat, tomato) ->
makeBurger(bun, meat, tomato))
.subscribeOn(
burger -> eatBurger(burger),
error -> complain(error));

67. 67
Start using
RxJava

68. 68
public Burger cook(){
// cooking is time consuming
// make sure it’s on a background thread
return burger;
}
Observable<Burger> burgerObservable =
Observable.fromCallable(this::cook)
.subscribeOn(Schedulers.computation())
.observeOn(AndroidSchedulers.mainThread())

69. 69
@GET(“repos”)
Call<List<Burger>> repoBurgers();
@GET(“repos”)
Observable<List<Burger>> repoBurgers();

70. 70

71. 7171
The ABCs of
RxJava
@FMuntenescu
jobs@upday.com
Building a Reactive Mindset
https://upday.github.io/blog/reactive_mindset_burgers
Reactive Burgers – Code Example
https://github.com/florina-muntenescu/ReactiveBurgers