When Scala came out few years ago, i was really impressed how you can do amazing things with so few line of codes. I was particularly impressed by the collection framework and all the lambda that was not possible until Java 8.

I start to read a book to learn basis and read articles on the web and in my opinion, this language could be the next language to move on.

Professionally, i got the opportunity to work with AKKA, an Agent framework developed in Scala: this gave to me my first occasion to play seriously with it.

But things goes on and projects required me to stay on plain old java dev.

Last week, Expedia has organized three days of conferences and workshop to let techies talk together and exchange ideas on tools and frameworks they are using. I was surprised that many teams were using Scala for their development, at least for the testing part through ScalaTest. During these three days, i have followed two 3-hours workshops – Scala 101 and Scala 201- which remind me how i found clever this language.

So i asked myself: how can i move to Scala, but this time for real?

To learn a new language, books are ok but you should use it for you day to day job in order to capture its philosophy and understand with real use case its strength and its weakness.

So i decided to move my current personal project to Scala: my Cthulhu Android game. Sounds difficult: first its an android app. Hopefully, i am using LibGDX so this should help me to move things out because i am not relying on android SDK. Second, i am using Gradle and Scala projects prefer using SBT.

So after few search on internet, some changes which were not working, it was not so complex to add Scala in my application:

  • Rename in the core project – the one with all the logic –  the src/main/java directory to src/main/scala. The plugin will allow you to mix Java and Scala files in this repository. I recommend you to do this to avoid compilation issues (which language is compiled first?)
  •  modify the gradle build file:
    • change plugin to apply plugin: 'scala'
    • add scala dependency
    • tweak scala plugin for better performance:
    • You will need to add Scala dependency in android module otherwise APK will not contain Scala library

The APK is bigger because of the Scala jar (+1.8Mo) but the game runs has if it was coded with java code. And that’s normal because Scala objects are compiled to java bytecode.

Some advices:

  • You can mix Java and Scala stuff pretty easily in order to move to Scala on some identified scope. Prefer classes with no inheritance to make thing simpler. Test your app to see if all is running well and then refactor bigger piece of code.\
  • You will not code properly in Scala because lot of things are different. Indeed you will code like in java but with some Scala words. But that’s ok: you will make mistakes, you will learn and you will change the way you code.
  • Try to make things working first and not search for beauty: when you mix java and Scala code, you will see some ugly code like MyClass$.MODULES in the java code when you want to get an instance of a case class. This is normal and until all is move to Scala this will not disappear. Don’t hesitate to create additional method to facilitate mixing things. This code will be removed at the end

In order to avoid issues to IDE make sure:

  • to clean .idea config folder
  • upgrade Intellij and Scala plugin to the last versions
  • upgrade gradle to 2.4.x+
  • re-import from scratch project in IntelliJ

adsGoogle Ads (aka AdMobs) is one of the most well known ad system used by developers to make some money with free apps/games. But other solutions exist and can be real alternatives.

I used to have some problems with revenues from Google Ads so i made some research and discovered App Flood.
The documentation on services proposed were clear and the “how-to” guide looked very clear and simple. So i decided to give a try to AppFlood in one of my LibGDX game.
After a quick registration on the web site to register my app and get my keys, i started implementing the API in my code. I was well surprised to see how much all is working out of the box and all the options proposed (banner, video ads, revenue on APK installation).
But how integrate an adsystem with a libgdx application?
Indeed with libgdx, the android application is just a wrapper to your main application in order to run it on android devices.
The adsystem should be plugged on the android layer through the application manifest
So first, add the required library in your android project:

  • Download somewhere the jar (as it will not be available on maven central repo)
  • and add the dependency:

Then following App flood doc, modify your AndroidManifest file:

The idea is to have a callback in your “core” code in order to call the ads system when you need to (for example screen transition).
So just create a simple interface for this in core module:

Modify your main application class to allow android application to registered the ad system:

Then implements this class in your Main android activity. Don’t forget to call the registering method on the main application.

Then whenever you decider you just have to call the method showAds() from your core code but dont forget to check if an ads system was registered otherwise you will get a NullPointerException

Sounds easy no?