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Compiling Android Apps

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ART History ● Android apps don’t run on the Java Virtual Machine (JVM) ● The first Android vm was called Dalvik. It had some problems. ● Nowadays, they run on a virtual machine called the Android Runtime (ART) ○ Remember when Oracle sued Google of Patent/Copyright infringement? ● ART makes certain affordances and optimizations for Android platform features and is actually quite different from the desktop JVM. ● For example: ○ JVM is a stack based architecture. ART is register based. ○ ART can elect to ahead-of-time compile an app at device install time.

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Optimized Builds The old way Kotlin source Java bytecode Optimized Java bytecode Optimized Dex bytecode kotlinc ProGuard (or DexGuard for $$$) DX (or recently D8)

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Aside: Naming things is hard.

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Optimized Builds The new way Kotlin source Java bytecode Optimized Dex bytecode kotlinc R8

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Why does this matter? ● Whole program optimization with nice Kotlin support ● Resource shrinking ● Tree shaking / 64k reference limit ● Bytecode obfuscation

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Non-Optimized Build: Left // Optimized Build: Right

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Goodbye classes2.dex 💥

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35% reduction of .apk size