RxJava + Android

From Charlotte Android Devs Meetup - 2/10/2015

Transcript

1. RxJava + Android Mike Drabic
2. RxJava is an implementation of the Observable pattern
3. Observables emit items. Observers aka Subscribers, consume items.
4. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 //todo
 }
 });
5. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 subscriber.onNext("one");
 subscriber.onNext("two");
 subscriber.onNext("three");
 subscriber.onCompleted();
 }
 });
6. Adhere to the terms of the Observable contract.
7. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 subscriber.onNext("one");
 subscriber.onNext("two");
 subscriber.onNext("three");
 subscriber.onCompleted();
 }
 });
8. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> sub) {
 subscriber.onNext("one");
 subscriber.onNext("two");
 subscriber.onNext("three");
 subscriber.onCompleted(); 
 }
 })
 .subscribe(/* observer, subscriber, or action implementations */);
9. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> sub) {
 subscriber.onNext("one");
 subscriber.onNext("two");
 subscriber.onNext("three");
 subscriber.onCompleted(); 
 }
 })
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 System.out.println("onNext(): " + s);
 }
 }, new Action1<Throwable>() {
 @Override
 public void call(Throwable throwable) {
 System.out.println("onError()");
 }
 }, new Action0() {
 @Override
 public void call() {
 System.out.println("onCompleted()!");
 }
 });
10. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> sub) {
 subscriber.onNext("one");
 subscriber.onNext("two");
 subscriber.onNext("three");
 subscriber.onCompleted(); 
 }
 })
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 System.out.println("onNext(): " + s);
 }
 }, new Action1<Throwable>() {
 @Override
 public void call(Throwable throwable) {
 System.out.println("onError()");
 }
 }, new Action0() {
 @Override
 public void call() {
 System.out.println("onCompleted()!");
 }
 }); onNext(): one onNext(): two onNext(): three onCompleted()
11. RxJava Example Some Organization’s REST API Get all members in the organization Get each member’s avatar
12. public class MemberService {
 
 public Observable<Member> getMembers() {
 //todo
 } public Observable<Bitmap> getAvatar(final Member member) { //todo }
 }
13. public class MemberService {
 
 public Observable<Member> getMembers() {
 return Observable.create(new Observable.OnSubscribe<Member>() {
 @Override
 public void call(Subscriber<? super Member> subscriber) { //todo make sure we emit items and complete //todo handle errors 
 }
 });
 } public Observable<Bitmap> getAvatar(final Member member) { //todo }
 }
14. public class MemberService {
 
 public Observable<Member> getMembers() {
 return Observable.create(new Observable.OnSubscribe<Member>() {
 @Override
 public void call(Subscriber<? super Member> subscriber) { //todo make sure we emit items and complete //todo handle errors 
 }
 });
 } public Observable<Bitmap> getAvatar(final Member member) { Observable.create(new Observable.OnSubscribe<Member>() {
 @Override
 public void call(Subscriber<? super Member> subscriber) { //todo make sure we emit items and complete //todo handle errors 
 }
 }); }
 }
15. public class MemberService {
 
 public Observable<Member> getMembers() {
 return Observable.create(new Observable.OnSubscribe<Member>() {
 @Override
 public void call(Subscriber<? super Member> subscriber) { //todo make sure we emit items and complete //todo handle errors }
 });
 } /* getAvatar() omitted */
 }
16. public class MemberService {
 
 public Observable<Member> getMembers() {
 return Observable.create(new Observable.OnSubscribe<Member>() {
 @Override
 public void call(Subscriber<? super Member> subscriber) { //todo make sure we emit items and complete //todo handle errors //getAllMembers sends HTTP request, parses response, etc List<Member> members = getAllMembers();
 }
 });
 } /* getAvatar() omitted */
 }
17. public class MemberService {
 
 public Observable<Member> getMembers() {
 return Observable.create(new Observable.OnSubscribe<Member>() {
 @Override
 public void call(Subscriber<? super Member> subscriber) { //todo make sure we emit items and complete //todo handle errors //getAllMembers sends HTTP request, parses response, etc List<Member> members = getAllMembers(); for (Member member : members) {
 subscriber.onNext(member);
 } subscriber.onCompleted();
 }
 });
 } /* getAvatar() omitted */
 }
18. public class MemberService {
 
 public Observable<Member> getMembers() { 
 return Observable.create(new Observable.OnSubscribe<Member>() { 
 @Override 
 public void call(Subscriber<? super Member> subscriber) {
 //todo handle errors
 //getAllMembers sends HTTP request, parses response, etc
 List<Member> members = getAllMembers();
 for (Member member : members) {
 subscriber.onNext(member); 
 }
 subscriber.onCompleted(); 
 } 
 }); }
 /* getAvatar() omitted */
 }

19. Subscribers are notified of errors via onError(Throwable)
20. public class MemberService {
 
 public Observable<Member> getMembers() { 
 return Observable.create(new Observable.OnSubscribe<Member>() { 
 @Override 
 public void call(Subscriber<? super Member> subscriber) {
 //todo handle errors
 //getAllMembers sends HTTP request, parses response, etc
 List<Member> members = getAllMembers();
 for (Member member : members) {
 subscriber.onNext(member); 
 }
 subscriber.onCompleted(); 
 } 
 }); }
 /* getAvatar() omitted */
 }

21. public class MemberService {
 
 public Observable<Member> getMembers() {
 return Observable.create(new Observable.OnSubscribe<Member>() {
 
 @Override
 public void call(Subscriber<? super Member> subscriber) {
 //todo handle errors
 try {
 //getAllMembers sends HTTP request, parses response, etc
 List<Member> members = getAllMembers();
 for (Member member : members) {
 subscriber.onNext(member);
 }
 subscriber.onCompleted();
 } catch (Exception e) {
 //todo
 }
 }
 });
 } /* getAvatar() omitted */ }
22. public class MemberService {
 
 public Observable<Member> getMembers() {
 return Observable.create(new Observable.OnSubscribe<Member>() {
 
 @Override
 public void call(Subscriber<? super Member> subscriber) {
 //todo handle errors
 try {
 //getAllMembers sends HTTP request, parses response, etc
 List<Member> members = getAllMembers();
 for (Member member : members) {
 subscriber.onNext(member);
 }
 subscriber.onCompleted();
 } catch (Exception e) {
 subscriber.onError(e); }
 }
 });
 } /* getAvatar() omitted */ }
23. public class MemberService {
 
 /* getMembers() omitted */ public Observable<Bitmap> getAvatar(final Member member) {
 return Observable.create(new Observable.OnSubscribe<Bitmap>() {
 
 @Override
 public void call(Subscriber<? super Bitmap> subscriber) {
 try {
 //getMemberAvatar sends request, and converts response to a bitmap. Bitmap avatar = getMemberAvatar(member);
 subscriber.onNext(avatar);
 subscriber.onCompleted();
 } catch (Exception e) {
 subscriber.onError(e);
 }
 } 
 });
 }
 }
24. RxJava ✓ Standard mechanism for error recovery
25. How can we combine these two Observables?
26. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers();
 //todo combine or chain these together
 Observable<Bitmap> avatarObservable = service.getAvatar(/* ??? */);
 }
 }
27. Operators!
28. Operators are a means to create, transform, filter, and combine Observables.
29. Create a sequence of observables with the FlatMap and Zip operator
30. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers();
 //todo combine or chain these together
 Observable<Bitmap> avatarObservable = service.getAvatar(/* ??? */);
 }
 }
31. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers();
 }
 }
32. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers(); 
 membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 //todo }
 }); }
 }
33. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers(); 
 membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 //todo }
 }); }
 }
34. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers(); 
 membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 //todo }
 }); }
 }
35. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers(); 
 membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 return Observable.zip(?, ?, ?); }
 }); } }
36. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers(); 
 membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) { Observable<Member> theMember = Observable.just(member);
 Observable<Bitmap> theAvatar = service.getAvatar(member);
 return Observable.zip(theMember, theAvatar, ?); }
 }); } }
37. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) { super.onCreate(savedInstance);
 Observable<Member> membersObservable = service.getMembers(); 
 membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 Observable<Member> theMember = Observable.just(member);
 Observable<Bitmap> theAvatar = service.getAvatar(member);
 Func2<Member, Bitmap, Member> zipFunc = getZipFunc();
 return Observable.zip(theMember, theAvatar, zipFunc); }
 }); } private Func2<Member, Bitmap, Member> getZipFunc() {
 return new Func2<Member, Bitmap, Member>() {
 @Override
 public Member call(Member member, Bitmap avatar) {
 member.setAvatar(avatar);
 return member;
 }
 };
 }
 }
38. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) {
 super.onCreate(savedInstance);
 //Get observable that will fetch all the members Observable<Member> membersObservable = service.getMembers(); //for each member, fetch the url, update the model, return the model membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 Observable<Member> theMember = Observable.just(member);
 Observable<Bitmap> theAvatar = service.getAvatar(member);
 Func2<Member, Bitmap, Member> zipFunc = getZipFunc();
 return Observable.zip(theMember, theAvatar, zipFunc);
 }
 });
 }
 
 private Func2<Member, Bitmap, Member> getZipFunc() {
 return new Func2<Member, Bitmap, Member>() {
 @Override
 public Member call(Member member, Bitmap avatar) {
 member.setAvatar(avatar);
 return member;
 }
 };
 } }
39. RxJava ✓ Standard mechanism for error recovery ✓ Multiple ways in which individual tasks can be composed
40. Time to update the UI with the results
41. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) {
 super.onCreate(savedInstance);
 //Get observable that will fetch all the members Observable<Member> membersObservable = service.getMembers(); //for each member, fetch the url, update the model, return the model membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 Observable<Member> theMember = Observable.just(member);
 Observable<Bitmap> theAvatar = service.getAvatar(member);
 Func2<Member, Bitmap, Member> zipFunc = getZipFunc();
 return Observable.zip(theMember, theAvatar, zipFunc);
 }
 });
 }
 
 private Func2<Member, Bitmap, Member> getZipFunc() {
 return new Func2<Member, Bitmap, Member>() {
 @Override
 public Member call(Member member, Bitmap avatar) {
 member.setAvatar(avatar);
 return member;
 }
 };
 } }
42. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) {
 super.onCreate(savedInstance);
 //Get observable that will fetch all the members Observable<Member> membersObservable = service.getMembers(); //for each member, fetch the url, update the model, return the model membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 Observable<Member> theMember = Observable.just(member);
 Observable<Bitmap> theAvatar = service.getAvatar(member);
 Func2<Member, Bitmap, Member> zipFunc = getZipFunc();
 return Observable.zip(theMember, theAvatar, zipFunc);
 }
 }) .subscribe(new Action1<Member>() {
 @Override
 public void call(Member member) {
 //adapter.add(member) which will update a ListView?
 }
 }, new Action1<Throwable>() {
 @Override
 public void call(Throwable throwable) {
 //show an AlertDialog to the user? 
 }
 });
 } /* getZipFunc() omitted */ }
43. Observable#subscribe() returns a Subscription
44. Subscriptions will leak memory if not unsubscribed
45. public class AnotherFragment extends Fragment {
 public void onCreate(Bundle savedInstance) {
 super.onCreate();
 Observable.just("Some long running work")
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 System.out.println(s);
 }
 });
 } //TODO - Fix leaky subscription!!!!
 }
46. public class AnotherFragment extends Fragment {
 
 private CompositeSubscription subscriptions = new CompositeSubscription();
 
 public void onCreate(Bundle savedInstance) {
 super.onCreate();
 Subscription subscription = Observable.just("Some long running work")
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 System.out.println(s);
 }
 });
 subscriptions.add(subscription);
 }
 
 public void onDestroy() {
 subscriptions.unsubscribe();
 super.onDestory();
 }
 }
47. RxJava ✓ Standard mechanism for error recovery ✓ Multiple ways in which individual task can be composed ✓ Hassle-free way of accessing a Context
48. On to the final feature
49. RxJava is synchronous by default.
50. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("Working on: " + threadId);
 subscriber.onNext("Hello");
 subscriber.onNext("World");
 subscriber.onCompleted();
 }
 })
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("onNext() Thread ID: " + threadId);
 }
 });
51. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("Working on: " + threadId);
 subscriber.onNext("Hello");
 subscriber.onNext("World");
 subscriber.onCompleted();
 }
 })
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("onNext() Thread ID: " + threadId);
 }
 }); Main/UI Thread ID: 1 Working on Thread ID: 1 onNext() Thread ID: 1 onNext() Thread ID: 1
52. observeOn(…) changes what thread the Subscriber observers on.
53. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("Working on Thread ID: " + threadId);
 subscriber.onNext("Hello");
 subscriber.onNext("World");
 subscriber.onCompleted();
 }
 })
 .observerOn(Schedulers.newThread())
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("onNext() Thread ID: " + threadId);
 }
 });
54. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("Working on Thread ID: " + threadId);
 subscriber.onNext("Hello");
 subscriber.onNext("World");
 subscriber.onCompleted();
 }
 })
 .observerOn(Schedulers.newThread())
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("onNext() Thread ID: " + threadId);
 }
 }); Main/UI Thread ID: 1 Working on Thread ID: 1 onNext() Thread ID: 11 onNext() Thread ID: 11
55. subscribeOn(…) changes what thread the Observable work will run on.
56. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("Working on Thread ID: " + threadId);
 subscriber.onNext("Hello");
 subscriber.onNext("World");
 subscriber.onCompleted();
 }
 })
 .subscribeOn(Schedulers.newThread()) .observeOn(Schedulers.newThread())
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("onNext() Thread ID: " + threadId);
 }
 });
57. Observable.create(new Observable.OnSubscribe<String>() {
 @Override
 public void call(Subscriber<? super String> subscriber) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("Working on Thread ID: " + threadId);
 subscriber.onNext("Hello");
 subscriber.onNext("World");
 subscriber.onCompleted();
 }
 })
 .subscribeOn(Schedulers.newThread())
 .subscribeOn(Schedulers.newThread())
 .subscribe(new Action1<String>() {
 @Override
 public void call(String s) {
 String threadId = String.valueOf(Thread.currentThread().getId());
 System.out.println("onNext() Thread ID: " + threadId);
 }
 }); Main/UI Thread ID: 1 Working on Thread ID: 12 onNext() Thread ID: 11 onNext() Thread ID: 11
58. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) {
 super.onCreate(savedInstance);
 //Get observable that will fetch all the members Observable<Member> membersObservable = service.getMembers(); membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 Observable<Member> theMember = Observable.just(member);
 Observable<Bitmap> theAvatar = service.getAvatar(member);
 Func2<Member, Bitmap, Member> zipFunc = getZipFunc();
 return Observable.zip(theMember, theAvatar, zipFunc);
 }
 }) .subscribe(new Action1<Member>() {
 @Override
 public void call(Member member) {
 //adapter.add(member) which will update a ListView?
 }
 }, new Action1<Throwable>() {
 @Override
 public void call(Throwable throwable) {
 //show an AlertDialog to the user? 
 }
 });
 } } }
59. public class MyFragment extends Fragment{
 private MemberService service;
 
 public void onCreate(Bundle savedInstance) {
 super.onCreate(savedInstance);
 //Get observable that will fetch all the members Observable<Member> membersObservable = service.getMembers(); membersObservable.flatMap(new Func1<Member, Observable<Member>>() {
 @Override
 public Observable<Member> call(Member member) {
 Observable<Member> theMember = Observable.just(member);
 Observable<Bitmap> theAvatar = service.getPhotoUrl(member);
 Func2<Member, Bitmap, Member> zipFunc = getZipFunc();
 return Observable.zip(theMember, theAvatar, zipFunc);
 }
 }) .subscribeOn(Schedulers.newThread()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new Action1<Member>() {
 @Override
 public void call(Member member) {
 //adapter.add(member) which will update a ListView?
 }
 }, new Action1<Throwable>() {
 @Override
 public void call(Throwable throwable) {
 //show an AlertDialog to the user? 
 }
 });
 } }
60. RxJava ✓ Standard mechanism for error recovery ✓ Multiple ways in which individual task can be composed ✓ Near hassle-free way of using a Context ✓ Easy control over thread scheduling
61. Go explore RxJava!
62. Questions?
63. Back Up
64. FlatMap applies a function to the output of a source observable and returns an observable that emits anything
65. List<String> nums = new ArrayList<>();
 nums.add("1");
 nums.add("2");
 nums.add("3");
 
 Observable.just(nums);
66. List<String> nums = new ArrayList<>();
 nums.add("1");
 nums.add("2");
 nums.add("3");
 
 Observable.just(nums)
 .flatMap(new Func1<List<String>, Observable<String>>() {
 @Override
 public Observable<String> call(List<String> nums) {
 return Observable.from(nums);
 }
 }) .subscribe(new Action1<String>() {
 @Override
 public void call(Integer s) {
 System.out.println("onNext():" + s);
 }
 });
67. List<String> nums = new ArrayList<>();
 nums.add("1");
 nums.add("2");
 nums.add("3");
 
 Observable.just(nums)
 .flatMap(new Func1<List<String>, Observable<String>>() {
 @Override
 public Observable<String> call(List<String> nums) {
 return Observable.from(nums);
 }
 }) .subscribe(new Action1<String>() {
 @Override
 public void call(Integer s) {
 System.out.println("onNext():" + s);
 }
 }); onNext(): 1 onNext(): 2 onNext(): 3
68. List<String> nums = new ArrayList<>();
 nums.add("1");
 nums.add("2");
 nums.add("3");
 
 Observable.just(nums)
 .flatMap(new Func1<List<String>, Observable<?>>() {
 @Override
 public Observable<?> call(List<String> nums) {
 //todo return whatever observable we want!!!
 }
 });
69. List<String> nums = new ArrayList<>();
 nums.add("1");
 nums.add("2");
 nums.add("3");
 
 Observable.just(nums)
 .flatMap(new Func1<List<String>, Observable<Integer>>() {
 @Override
 public Observable<Integer> call(List<String> nums) { List<Integer> asInts = new ArrayList<>();
 for (String num : nums) {
 asInts.add(Integer.parseInt(num));
 }
 return Observable.from(asInts);
 }
 }) .subscribe(new Action1<Integer>() {
 @Override
 public void call(Integer integer) {
 System.out.println("onNext():" + integer.toString());
 }
 }); onNext(): 1 onNext(): 2 onNext(): 3
70. Zip combines the emissions of two or more observables via a function and returns an observable that emits the result of this function.
71. Combines the emissions of two or more observables
72. Returns an observable that emits a single item of your choosing.
73. Observable<Integer> numbers = Observable.just(1, 2, 3);
 Observable<String> letters = Observable.just("A", "B", “C"); 
 Observable.zip(numbers, letters, new Func2<Integer, String, SimpleEntry>() {
 @Override
 public SimpleEntry<Integer, String> call(Integer key, String value) {
 return new SimpleEntry<>(key, value);
 }
 })
 .subscribe(new Action1<SimpleEntry>() {
 @Override
 public void call(SimpleEntry entry) {
 System.out.println(entry.getKey() + " :: " + entry.getValue());
 }
 });
74. Observable<Integer> numbers = Observable.just(1, 2, 3);
 Observable<String> letters = Observable.just("A", "B", “C"); 
 Observable.zip(numbers, letters, new Func2<Integer, String, SimpleEntry>() {
 @Override
 public SimpleEntry<Integer, String> call(Integer key, String value) {
 return new SimpleEntry<>(key, value);
 }
 })
 .subscribe(new Action1<SimpleEntry>() {
 @Override
 public void call(SimpleEntry entry) {
 System.out.println(entry.getKey() + " :: " + entry.getValue());
 }
 });
75. Observable<Integer> numbers = Observable.just(1, 2, 3);
 Observable<String> letters = Observable.just("A", "B", “C"); 
 Observable.zip(numbers, letters, new Func2<Integer, String, SimpleEntry>() {
 @Override
 public SimpleEntry<Integer, String> call(Integer key, String value) {
 return new SimpleEntry<>(key, value);
 }
 })
 .subscribe(new Action1<SimpleEntry>() {
 @Override
 public void call(SimpleEntry entry) {
 System.out.println(“OnNext(): ” + entry.getKey() + " :: " + entry.getValue());
 }
 }); onNext(): 1 :: A onNext(): 2 :: B onNext(): 3 :: C