Every new language aspires to abstract complexity using neat syntax or cool features. Kotlin is no different. Yet knowing how it works under the hood can bring benefits to developers. I will explore how Kotlin ends up as machine code and how we can leverage that knowledge. First, let’s talk about Kotlin performance faux pas that developers make and how you can easily discover and prevent them. Next, I will mention the differences between the JVM, Dalvik and Android Runtime (ART) and how Android system optimizes your applications without you even knowing. Finally, we will focus on how you can improve performance and reliability of your application when working with ART and what optimizations you get for free from the system. After this presentation, you will have a better understanding how to write more performant Kotlin and Java so your users will have even more sublime app experience.

1. typealias `The Talk`
=
(Kotlin) -> `Machine Code`
Tomek Polański

2. Code issues

3. class Sum(val number: Int) {
fun add(): Int = number + 2
}

4. class Sum(private val number: Int) {
fun add(): Int = number + 2
}

5. fun convert(list: List<Int> = (1..1_000_000).toList()) =
list.map { it + 1 }
.mapIndexed { index, it -> "Number at $index is $it" }

6. Decompiled code

7. public static List<String> convert(List<Integer> list) {
Collection<Integer> dest = new ArrayList<>(list.size());
Iterator<Integer> iterator = list.iterator();
while (iterator.hasNext()) {
dest.add(iterator.next() + 1);
}

8. List<String> result = new ArrayList<>(dest.size());
Iterator<Integer> iter2 = dest.iterator();
int index = 0;
while (iter2.hasNext()) {
result.add("Number at " + index++ + " is " + iter2.next());
}
return result;
}

9. When is it useful?

10. ● Investigating Performance
Issues
Decompiled Code

11. ● Access Modifiers
Decompiled Code

12. fun convert(list: List<Int> = (1..1_000_000).toList()) =
list.map { it + 1 }
.mapIndexed { index, it -> "Number at $index is $it" }

13. fun convert(list: List<Int> = (1..1_000_000).toList()) =
list.asSequence()
.map { it + 1 }
.mapIndexed { index, it -> "Number at $index is $it" }
.toList()

14. List<String> convert(List<String> list) {
return SequencesKt.toList(
SequencesKt.mapIndexed(
SequencesKt.map(
CollectionsKt.asSequence(list),
(Function1)null.INSTANCE),
(Function2)null.INSTANCE));
}

15. List<String> convert(List<String> list) {
return SequencesKt.toList(
SequencesKt.mapIndexed(
SequencesKt.map(
CollectionsKt.asSequence(list),
(Function1)null.INSTANCE),
(Function2)null.INSTANCE));
}

16. List<String> convert(List<String> list) {
return SequencesKt.toList(
SequencesKt.mapIndexed(
SequencesKt.map(
CollectionsKt.asSequence(list),
(Function1)null.INSTANCE),
(Function2)null.INSTANCE));
}

17. List<String> convert(List<String> list) {
return SequencesKt.toList(
SequencesKt.mapIndexed(
SequencesKt.map(
CollectionsKt.asSequence(list),
(Function1)null.INSTANCE),
(Function2)null.INSTANCE));
}

18. List<String> convert(List<String> list) {
return SequencesKt.toList(
SequencesKt.mapIndexed(
SequencesKt.map(
CollectionsKt.asSequence(list),
(Function1)null.INSTANCE),
(Function2)null.INSTANCE));
}
?!
?!

19. Java Bytecode

20. class MyClass(val number: Int) {
fun add() = number + 2
}
Kotlin

21. public final add()I
ALOAD 0
GETFIELD package/MyClass.number:I
ICONST_2
IADD
IRETURN
class MyClass(val number: Int) {
fun add() = number + 2
}
Kotlin JVM Bytecode

22. LDC "Number at"
INVOKEVIRTUAL java/lang/StringBuilder.append Ljava/lang/StringBuilder;
LDC " is "
INVOKEVIRTUAL java/lang/StringBuilder.append Ljava/lang/StringBuilder;

23. When is it useful?

24. ● Knowing the Real Code
Java Bytecode

25. Dalvik Bytecode

26. Registers
Cache
RAM

27. Registers
Cache
RAM
2ns
5ns - 50ns
90ns

28. .method public final add()I
.registers 2
iget v0, p0, Lpackage/MyClass; ->number:I
add-int/lit8 v0, v0, 0x2
return v0
class MyClass(val number: Int) {
fun add() = number + 2
}
Kotlin DVM Bytecode

29. .method public final add()I
.registers 2
iget v0, p0, Lpackage/MyClass; ->number:I
add-int/lit8 v0, v0, 0x2
return v0
DVM Bytecode
public final add()I
ALOAD 0
GETFIELD package/MyClass.number:I
ICONST_2
IADD
IRETURN
JVM Bytecode

30. When is it useful?

31. ● Preparing Dalvik Presentation
Dalvik Bytecode

32. ● Previewing APKs
Dalvik Bytecode

33. typealias `The Talk`
=
(Kotlin) -> `Machine Code`

34. Let’s talk about ART

35. Android Runtime
KitKat
4.4
Lollipop
5.0
(experimental) (replacement)

36. Dex to Machine
Interpreter JIT AOT

37. Interpreter
Running app
Interpreter
Interpreter
Interpreter

38. Interpreter
Always available but
slow

39. Just In Time
Running app
JIT

40. Just In Time
Fast but must
kick in

41. Ahead of Time
JIT AOT+ =Interpreter

42. Ahead of Time
Running app
Profiling
Idle
AOT

43. Developer Compilation
.class .dexKotlin

44. Android Compilation
Interpreter
JIT
AOT
Machine
code

45. ART for Developers

46. ART for Developers
Memory
locality

47. ART for Developers
Memory
locality
Loop
speed

48. ART for Developers
Memory
locality
Loop
speed
Concurrent
GC

49. Things to remember

50. Decompile your code

51. ART is Cool!

52. Thank you!
Tomek Polański
@tpolansk

53. Recommended read
● ART + Dalvik Overview
(goo.gl/cXuhe1)

54. References
● Google I/O 2014 - The ART runtime
● Deep dive into Android Multidex
● Next-generation Dex Compiler Now in Preview
● Differences between .class and .dex files in
Java & Android
● Why understand bytecode