J2ObjC. The silver bullet in cross-platform mobile development

J2ObjC. The silver bullet in cross-platform mobile development

The war between mobile platforms is over. After several years of active competition, we’ve got two operating systems with almost the same quality and feature set. The closest competitors of Android and iOS are far behind in market share. For us, as mobile developers, it means that all further projects should target at least two platforms. Main products we are working on at GetSocial are 3 SDKs for Android, iOS and Unity. All libraries have the same functionality and feature rich UI. In this talk, I want to share results of our internal RnD experiments with j2objc – Java to Objective-C translation tool developed by Google. J2objc goal is to write an app’s non-UI code (such as application logic and data models) in Java, which is then shared with no editing by Android and iOS apps.


Vitaliy Zasadnyy

February 18, 2016


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    #MobOS2016 The silver bullet in cross-platform mobile development J2ObjC Vitaliy

    Zasadnyy Head of Mobile @ GetSocial February 18-19, 2016, Cluj
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    In yellow boxes like this one you can find comments

    to the slide. Enjoy the presentation and if you have any questions, feel free to reach me at v@zasadnyy.com
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    #MobOS2016 Chronology: - April 2012, GDG Lviv was born -

    September 2012, Google announced J2ObjC - October 2012, Googlers were late for 4 hours to our event; to fill the gap I had my fist talk about J2ObjC
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    With help of GetSocial SDK you can add Activity Feed,

    Chat, Notifications or Smart Invites just with a few lines of code
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    With over 50 integrated apps, GetSocial serve 20 million users every month that generated half a billion sessions during 2015.
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    Android Bridge C# API Unity SDK Java Objective C C# We have Android and iOS SDKs built natively using Java and Objective C respectively. Unity SDK is a thin bridge layer that forwards calls from public interface exposed in C# to native implementation
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    leverage all platform features PROS: • doing work twice • hard to keep in sync API behaviour CONS: The biggest advantage of having pure native SDK - being able to use low level platform features. Disadvantage - all features are implemented twice (longer time to market), also it’s hard to keep behaviour in sync, coz each developer has unique way to solve problems.
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    –Sun Microsystems WRITE ONCE, RUN EVERYWHERE “ We decided to

    look around on possible solutions, to reach ultimate goal, write code once and run it everywhere.
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    #MobOS2016 REQUIREMENTS Maintainability Performance Size footprint Licensing Requirements for the

    solution: - performance should be at least the same as on native - code should be easy to maintain (reliable toolchain) - SDK should keep reasonable size - ideally solution should be free and compatible with our distribution model
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    #MobOS2016 Xamarin Pros: proven technology, big community, access to UI

    API from Xamarin Cons: it’s not possible to build SDK with Xamarin and use with native apps; paid solution
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    #MobOS2016 RoboVM The most recent tool made by startup based

    in Finland. Pros: you can use any JVM language, code is cross compiled to iOS machine code => fast, gives access to UI API Cons: very early stage, no big apps using it, paid solution
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    #MobOS2016 J2ObjC Project started and actively developed by Google. Inbox

    built with J2ObjC. We started an internal RnD project to research if J2ObjC can fit with our requirements.
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    #MobOS2016 • NOT cross-platform application tool • NOT platform-independent UI

    toolkit • NOT Java emulator • NOT one time source translation WHAT J2OBJC ISN’T
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    #MobOS2016 IS IT PRODUCTION READY? 25+ projects Google is using

    J2ObjC for almost all office apps. Besides Google, more than 25 projects claimed using J2ObjC.
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    #MobOS2016 WHAT IS SUPPORTED? • Full Java 7 syntax •

    Inner classes, enums, annotations… • Reflection (almost all) • OSNI code embedding J2ObjC engineers did a great job, they reimplemented Java paradigms like inner classes, enums, annotations and reflection on Objective C, where they are not available.
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    #MobOS2016 OSNI CODE EMBEDDING static native void log(String text) /*-[

    NSLog(@"%@", text); 
 ]-*/; JAVA + (void)log: (NSString*)text {
 NSLog(@"%@", text); 
 } OBJECTIVE C You can embed Objective C code in Java in a special comments. DON’T do that, little bunnies die each time you’re using OSNI.
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    #MobOS2016 HOW TO USE $ j2objc Romobos.java BASH • Romobos.java

    $ ls Romobos.h Romobos.m BASH translating Romobos.java Translated 1 file: 0 errors, 0 warnings j2objc is a command line tool, you’re going to work with to perform translation from Java to Objective C. It’s very powerful, but not very convenient to use on a real projects, coz amount of passed parameters will explode.
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    #MobOS2016 AVAILABLE PLUGINS Make Maven Eclipse Gradle J2ObjC provide a

    plugins for most part of popular build tools. We’re going to focus on Gradle plugin.
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    DEMO IS AVAILABLE ON GITHUB Links on the SpeakerDeck are

    not clickable, so: https://github.com/zasadnyy/j2objc-reddit-prototype
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    #MobOS2016 NAME MANGLING package com.zasadnyy.reddit.model; public class RedditDataManager {…} RedditDataManager.java

    @interface ComZasadnyyRedditModelRedditDataManager : NSObject RedditDataManager.h Translates to CLASS NAMES Check the demo repo for more examples.
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    #MobOS2016 NAME MANGLING MAKE IT READABLE Option 1: Create a

    Facade class to wrap public interface During cross compilation some Java classes are mapped to analogues on ObjC side, e.g. String => NSString. But not all, e.g. ArrayList => JavaLangArrayList. Most part of JRE classes are translated so on ObjC side developer forced to work with Java-like interface. And it’s very inconvenient. Solution: provide a facade for a public interface.
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    #MobOS2016 NAME MANGLING MAKE IT READABLE Option 2: Provide method/package

    mapping configurations Partially you can solve problem by providing package/ method name mapping. In reality you’ll use combination of two approaches.
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    #MobOS2016 NAME MANGLING MAKE IT READABLE j2objcConfig {
 translateArgs '--prefixes',

 translateArgs '--mapping', 'methodMapping.properties'
 } shared/build.gradle Provide method/package mapping configurations
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    #MobOS2016 JAVA RUNTIME ENVIRONMENT • Based on Android JRE •

    Almost 2000 classes ported • iOS-specific native code • Covered with over 4K Unit test THE JRE_EMUL PROJECT soon…
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    #MobOS2016 UNIT TESTING IS DNA • JUnit 3, 4 supported

    • Harmcrest 1.3 • Mockito 1.9.5 J2ObjC approach to validate generated code One the first features of J2ObjC was ability to translate Unit tests.
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    #MobOS2016 MEMORY MANAGEMENT There is no garbage collector on Objective

    C Solution approaches: • Reference Counting • ARC
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    #MobOS2016 MEMORY MANAGEMENT REFERENCE LOOPS R Objective C: ref count

    != 0, so keep A and B in memory B A REF COUNT = 1 REF COUNT = 1
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    @Weak and @WeakOuter annotations Provided tools:
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    #MobOS2016 PERFORMANCE Make simple computations on the array of 600

    GPS coordinates 1,000 times Testing method: COMPUTATIONAL Source: Medium post by Harry Cheung
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    #MobOS2016 PERFORMANCE COMPUTATIONAL Average iOS Computational Performance Swift 1.2 J2ObjC

    J2ObjC (ARC) Xamarin RoboVM RubyMotion Time, s 0 7,5 15 22,5 30 RubyMotion is slow a hell. Let’s drop it from the graph.
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    #MobOS2016 PERFORMANCE COMPUTATIONAL Average iOS Computational Performance Swift 1.2 J2ObjC

    J2ObjC (ARC) Xamarin RoboVM Time, s 0 0,275 0,55 0,825 1,1 J2ObjC is more performant than Swift.
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    #MobOS2016 PERFORMANCE Make simple computations on the array of 600

    GPS coordinates 10,000 times Testing method: MEMORY Source: Medium post by Harry Cheung
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    #MobOS2016 PERFORMANCE Peak iOS Memory Performance Swift 1.2 J2ObjC J2ObjC

    (ARC) Xamarin RoboVM RubyMotion Usage, Mb 0 5,5 11 16,5 22 MEMORY Regarding memory performance is more or less similar to Swift. RoboVM is doing some magic:)
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    #MobOS2016 IOS APP SIZE IMPACT 3Mb Extra (1 target platform)

    Reduce size: • Include only required parts of jre_emul.a • Shrink unused Java code with Proguard 3Mb is mainly a size of translated JRE library that should be included with your project.
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    #MobOS2016 ARCHITECTURE FOLDER STRUCTURE workspace ├── build.gradle ├── android │

    ├── build.gradle │ └── src/... // only Android specific code ├── ios │ ├── IOS-APP.xcodeproj │ ├── Podfile │ ├── WORKSPACE.xcworkspace │ ├── IOS-APP/... │ ├── IOS-APPTests/... │ └── Pods/... └── shared ├── build.gradle // ‘j2objc' plugin configuration ├── build/.. // generated build folder ├── lib/.. └── src/... // shared code for translation
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    #MobOS2016 ARCHITECTURE GETSOCIAL FOLDER STRUCTURE workspace ├── build.gradle ├── android-client

    // only presentation code │ └── … ├── android-library // platform dependant implementations │ └── … ├── ios │ └── … └── shared └── …
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    #MobOS2016 UI ARCHITECTURE Implementation Domain CLEAN ARCHITECTURE Dependency Rule Using

    J2ObjC forces you to have a nice “clean” architecture. Learn more…
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    #MobOS2016 MISSING: AssertJ, RxJava, http libraries, DI, … • Only

    few 3rd party libraries are ported PORTED: Junit, Hamcrest, Mockito, Protobuf, Guava, Gson, Joda-time, commons-lang3, sqlighter-4 Check ported libs at j2objc-common-libs-e2e-test GitHub project LIMITATIONS
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    #MobOS2016 LIMITATIONS • Porting new libraries requires sources • Not

    all JRE is supported • Only Java 7 can be used • All team members should know iOS and Android • Only few 3rd party libraries are ported
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    #MobOS2016 IS IT THE SILVER BULLET? J2ObjC is an evolution

    of idea of cross platform development. For Google it works quite good. For GetSocial J2ObjC is pretty much a silver bullet, as it solves most part of problems we had. Is it a silver bullet for you? Before using any tool you should always check if it applicable in your particular case. To sum up, don’t be afraid to play with new tools, experiment, fail, try again, find your silver bullet solutions and absolutely go cross-platform. Thank you.
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    #MobOS2016 RESOURCES • Official J2ObjC website: http://j2objc.org • J2ObjC on

    GitHub: https://github.com/google/j2objc • J2ObjC Gradle Plugin on GitHub: https://github.com/j2objc-contrib/j2objc-gradle • GitHub project with end-to-end test of compatible libraries: https://github.com/j2objc-contrib/j2objc-common-libs-e2e-test • Goodow GitHub account with several J2ObjC related repos: https://github.com/goodow • Cross platform frameworks performance tests: http://bit.ly/crossplatformTests • Demo project: https://github.com/zasadnyy/j2objc-reddit-prototype