Using Java 8 on Android
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The document discusses the introduction of Java 8 features on Android, noting that many are only available from Android N onwards. Key aspects include the new time API, lambda functions, method references, and default methods for interfaces, along with a comparison of the Jack toolchain and Retrolambda for compatibility with earlier Java versions. It emphasizes improved code simplicity and functionality through features like streams and new APIs for handling collections and dates.
Using Java 8 on Android
- 1. Using Java 8 on Android Eduardo Bonet
- 2. Motivation Java 8 was released over 2 years ago, bringing many new features, but that are not yet availabe on Android. The new Jack & Kill toolchain brought us some official Java 8 support, but some features are only available after Android N and others were left aside.
- 3. Java 8 Much less verbose. New API's: java.time.* java.util.stream.* java.util.function.* Language changes: Default Methods and static methods for interfaces Lambda Functions Method References
- 4. Streams Improved API for dealing with collections, also making parallelization much easier. // Java 7 names = new ArrayList<>(); for (Person p : people) { if(p.age > 16) names.add(p.name); } // Java 8 names = people.stream() .filter(p -> p.age > 16) .map(p -> p.name) .collect(Collectors.toList());
- 5. Time API New API to deal with date and time, fully replacing java.util.Calendar and java.util.Date. // Java7 Date date, datePlusThreeDays; date = new GregorianCalendar(2014, Calendar.FEBRUARY, 11).getTime() Calendar c = Calendar.getInstance(); c.setTime(date); c.add(Calendar.DATE, 3) datePlusThreeDays = c.getTime() // Java 8 LocalDate otherDate, otherDatePlusThreeDays; otherDate = LocalDate.of(2014, Month.FEBRUARY, 11); otherDatePlusThreeDays = otherDate.plus(3, ChronoUnit.DAYS);
- 6. Lambda Functions Lambda Functions are a easier and cleaner way to create objects that implement a single method interface, i. e., Functors. // Java 7 v.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Log.d(TAG, "onClick: "); } }); // Java 8 Lambda v.setOnClickListener(view -> Log.d(TAG, "onClick: "));
- 7. Observable.from(people) .filter(new Func1<Person, Boolean>() { @Override public Boolean call(Person person) { return person.age > 16; } }) .map(new Func1<Person, String>() { @Override public String call(Person person) { return person.name; } }) .subscribe(new Action1<String>() { @Override public void call(String s) { System.out.println(s); } }); Observable.from(people) .filter(person -> person.age > 16) .map(person -> person.name) .subscribe(s -> System.out.println(s));
- 8. Method References Method References are an even simpler version of Lambda Functions, where arguments are simply passed on to another function. Observable.from(people) .filter(person -> person.age > 16) .map(person -> person.name) .subscribe(System.out::println); // .subscribe(s -> System.out.println(s));
- 9. Try-with-resources Better Syntax for objects that must be closed after use (they must implement the Closeable interface). // Java 7 BufferedReader br = new BufferedReader(new FileReader(path)); try { System.out.println(br.readLine()); } finally { if (br != null) br.close(); } // Java 8 try (BufferedReader br = new BufferedReader(new FileReader(path))) { System.out.println(br.readLine()); }
- 10. Default Methods for Interfaces interface Vehicle { default void print(){ System.out.println("I am a vehicle!"); } } class Car implements Vehicle { public void print(){ Vehicle.super.print(); System.out.println("I am a car!"); } } class Boat implements Vehicle { }
- 11. Bringing Java 8 to Android
- 12. Jack New Android tool that transforms .java into .dex Introduced on Android N. Suports Lambda Functions and Method References on all Android versions. Suports Default Methods and Streams only for Android 24+ Does nto support java.time.*
- 13. Streams: LightweightStreams Streams API implementation using Java 7 Collections. List<String> names = Stream.of(people) .filter(p -> p.age > 16) .map(p -> p.name) .collect(Collectors.toList()); Method Count: 719 (1.1.2)
- 14. Streams: RxJava Observables are fundamentally different from Streams (push vs. pull), but similar functionality can be obtained using Observable.from(myCollection). List<String> names = Observable.from(people) .filter(p -> p.age > 16) .map(p -> p.name) .toList().toBlocking().first(); Method Count: 5492 (1.1.8)
- 15. Streams // Stream people.stream() .filter(p -> p.age > 16) .map(p -> p.name) .collect(Collectors.toList()); // LightweightStreams Stream.of(people) .filter(p -> p.age > 16) .map(p -> p.name) .collect(Collectors.toList()); // RxJava Observable.from(people) .filter(p -> p.age > 16) .map(p -> p.name) .toList().toBlocking().first();
- 16. java.time.*: ThreeTenABP optimized version for Android. Same API as java.time.*, making them interchangeable. Method Count: 3280 ThreeTenBP
- 17. Retrolambda Transforms Java 8 code into code compatible with Java 5, 6 and 7. Operates during compile time. Full support to Lambdas, Try-With-Resources and Method References. Partial support to default methods.
- 19. Resumo RL Jack RxJava LS TT Streams 24+ ✔ ✔ Default Methods Partial 24+ Lambda ✔ ✔ Method References ✔ ✔ Try-With-Resources ✔ ✔ java.time.* ✔ - RL: Retrolambda, LS: LightweightStreams, TT: ThreeTenABP
- 20. References Jack Jack e Java 8 Retrolambda Lightweight Stream ThreeTenABP Estudo sobre API para date RxJava Retrolambda vs Jack
- 21. Thanks Questions? | |blog github linkedin