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Destination: 

- “Sometimes its the journey that teaches you a lot about your destination.” Destination: 

Bon Voyage!! • Aim: To compile your Android Code. • Material required: Java files, AndroidManifest.xml, resources, assets(optional) • Procedure: Step 1: Your .java files or .kt files gets converted to .class files that is the ByteCode through “javac” or “kotlinc” command. 

MainActivity.java File: MainActivity.class ByteCode: 

ByteCode Execution of: c = 2 * (a+b) • iConst 2 • iLoad a • iLoad b • iAdd • iMul • iStore c a b 42 7 C 0 2 

ByteCode Execution of: c = 2 * (a+b) • iConst 2 • iLoad a • iLoad b • iAdd • iMul • iStore c a b 42 7 C 0 2 42 

ByteCode Execution of: c = 2 * (a+b) • iConst 2 • iLoad a • iLoad b • iAdd • iMul • iStore c a b 42 7 C 0 2 42 7 

ByteCode Execution of: c = 2 * (a+b) • iConst 2 • iLoad a • iLoad b • iAdd • iMul • iStore c a b 42 7 C 0 2 49 

ByteCode Execution of: c = 2 * (a+b) • iConst 2 • iLoad a • iLoad b • iAdd • iMul • iStore c a b 42 7 C 0 98 

ByteCode Execution of: c = 2 * (a+b) • iConst 2 • iLoad a • iLoad b • iAdd • iMul • iStore c a b 42 7 C 98 

• Android does not use this .class file directly. Android has its own byte code format and its own virtual machine that is Dalvik Virtual Machine. • Multiple .class files or class files from any .jar file gets converted to a single classes.dex file. • Dx tool from the build platform tools inside Android SDK converts multiple .class files into single classes.dex . 

MainActivity.dex MainActivity.java Dx: --dex --output MainActivity.dex 

Dalvik code of int foo = 1+2 const-1 r0 1 foo Dest Arg0 Arg1 

Dalvik code of int foo = 1+2 const-1 r0 1 add-int/lit8 r1 Foo Arg1 Arg0 Dest 

Dalvik code of int foo = 1+2 const-1 r0 1 add-int/lit8 r1 Foo r0 2 Dest Arg0 Arg1 

Dalvik code of int foo = 1+2 const-1 r0 1 add-int/lit8 r1 Foo r0 2 1 Dest Arg0 Arg1 

Dalvik code of int foo = 1+2 const-1 r0 1 add-int/lit8 r1 Foo r0 2 1 1+2 Dest Arg0 Arg1 

Building a story from Why? - “The art and science of asking questions is the source of all knowledge. The more you ask the more you know” • Why does Android not use .class files? • Why does Android not use JVM? 

Types of Virtual Machine • Virtual machine is a software environment that can be an emulator, an operating system or complete hardware virtualization, that has implementation of resources without the actual hardware. • Two types of VM on basis of architecture: Stack Based architecture and Register Based Architecture. 

Types of Virtual Machine • Virtual machine is a software environment that can be an emulator, an operating system or complete hardware virtualization, that has implementation of resources without the actual hardware. • Two types of VM on basis of architecture: Stack Based architecture and Register Based Architecture. • And yes, from previous examples you guessed right: JVM: Stack Based Architecture DVM: Register Based Architecture 

Let’s look numbers • Study on different VM shows that register based architecture requires an 47% less executed VM instructions than stack based. • Register based code is 25% larger in code size than the corresponding stack based code but this overall effects around 1.05% on load of VM. • So overall performance is that Dalvik VM is taking 32.3 % less time to execute standard benchmarks. • Licensing issues from Sun side which also led to have conflicts and thus Android took another VM. • Used because of memory limitations, reduce system overhead, redundancies and bringing optimization to .class files. - And you will have the answer to WHY? 1 2 3 Dalvik VM JVM 

.class . . . . . . . . .class .class .class . . 

.class . . . . . . . . .class .class .class . . classes.dex 

Step 2: Resources Prepared • Drawables (all dpis: xxhdpi, mdpi, xhdpi, hdpi) • Layout files • Menu files (optional) • Anim folder • raw • Color • Styles 

Putting it all together • Material 3: Android asset Packaging Tool. • It allows to create, update zip compatible archive (apk, zip, jar). It can also compile resources into binary assets. • Printing permissions, printing resources, print configurations supported. • Step 3: aapt zip classes.dex, resources and AndroidManifest.xml into a zip archive called APK. 

The Final picture to the APK 

Installation Dalvik ART ??? 

Dalvik • Based on JIT (Just in Time) Compilation • Every time your app runs, part of code important for its execution is going to be translated to machine code at that moment. Further caching while app is running. • DEX to ODEX conversion and copy to dalvik-cache. • Optimizations: • Replace method index with vtable index • Replace field index with byte offset • Replacement with inline calls • Cut Empty methods 

ART: The next level • Based on AOT (Ahead of time) compilation. • Perform dex2oat to have a elf file. • Solved garbage collection issues. • Improved battery performance as power to interpret line by line is saved. 

Installation Picture 

Thank you !