Jack and Jill are new build tools introduced by Google that optimize the Android build process. Jack compiles Java code to an intermediate format called Jayce bytecode. Jill then compiles Jayce to optimized Dalvik bytecode. This results in faster build times, smaller app sizes, and support for Java 8 language features on older Android versions. It also allows for new optimizations from tools like ProGuard and DexGuard during the build. The changes improve performance for developers and applications.

1. The Jack and Jill
build system
Eric Lafortune
Developer of ProGuard and DexGuard
CTO at GuardSquare
www.guardsquare.com

2. The Jack and Jill build system
Inside the build system
and the runtime
Practical implications and
results

3. Jack and Jill
Java Android Compiler Kit
Jack Intermediate Library Linker

4. Jack and Jill
● Now default in build process of AOSP
● Optional in Gradle build process:
android {
defaultConfig {
useJack true
...
}
...
}
android {
defaultConfig {
useJack true
...
}
...
}
com.android.tools.build:gradle:2.0.0

5. android {
defaultConfig {
jackOptions {
enabled true
jackInProcess true
}
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
...
}
...
}
android {
defaultConfig {
jackOptions {
enabled true
jackInProcess true
}
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
...
}
...
}
Jack and Jill
com.android.tools.build:gradle:2.1.0 alpha1

6. android {
defaultConfig {
jackOptions {
enabled true
jackInProcess true
}
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
...
}
...
}
android {
defaultConfig {
jackOptions {
enabled true
jackInProcess true
}
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
...
}
...
}
Jack and Jill
...
:generateReleaseSources
:jillReleasePackagedLibraries
:jillReleaseRuntimeLibraries
:processReleaseJavaRes UP-TO-DATE
:transformResourcesWithMergeJavaResForRelease
:compileReleaseJavaWithJack
:compileReleaseNdk UP-TO-DATE
:compileReleaseSources
...
...
:generateReleaseSources
:jillReleasePackagedLibraries
:jillReleaseRuntimeLibraries
:processReleaseJavaRes UP-TO-DATE
:transformResourcesWithMergeJavaResForRelease
:compileReleaseJavaWithJack
:compileReleaseNdk UP-TO-DATE
:compileReleaseSources
...
com.android.tools.build:gradle:2.1.0 alpha1

7. Why?
Technical
Legal ?
Strategical ?

8. Android build process
Java bytecode
(.class)
Libraries
(.class)
Dx
Javac
Source code
(.java)
Libraries
(.class)
XML resources
(.xml)
Assets Assets
Compiled
XML resources
(.xml)
Aapt
Dalvik bytecode
(classes.dex)
Android
runtime stubs
(.class)

9. Transform API
Java bytecode
(.class)
Processor
Libraries
(.class)
Transformed
Java bytecode
(.class)
Dx
Javac
Assets
Compiled
XML resources
(.xml)
Aapt
Dalvik bytecode
(classes.dex)
Source code
(.java)
Libraries
(.class)
XML resources
(.xml)
Assets
Runtime stubs
(.class)

10. ProGuard
Java bytecode
(.class)
ProGuard
Libraries
(.class)
Optimized
Java bytecode
(.class)
Dx
Javac
Assets
Compiled
XML resources
(.xml)
Aapt
Dalvik bytecode
(classes.dex)
ProGuard
config
(.txt)
ProGuard
mapping
(.txt)
Source code
(.java)
Libraries
(.class)
XML resources
(.xml)
Assets
Runtime stubs
(.class)

11. ProGuard
Java bytecode
(.class)
ProGuard
Libraries
(.class)
Optimized
Java bytecode
(.class)
Dx
Javac
Assets
Compiled
XML resources
(.xml)
Aapt
Dalvik bytecode
(classes.dex)
ProGuard
config
(.txt)
ProGuard
mapping
(.txt)
Source code
(.java)
Libraries
(.class)
XML resources
(.xml)
Assets
Runtime stubs
(.class)

12. Jack and Jill
Libraries
(.jayce)
Jack
Assets
Compiled
XML resources
(.xml)
Aapt
Dalvik bytecode
(classes.dex)
ProGuard
config
(.txt)
ProGuard
mapping
(.txt)
Source code
(.java)
Libraries
(.class)
XML resources
(.xml)
Assets
Runtime stubs
(.class)
Jill
Jill Runtime
(.jayce)

13. Code representations
for (int i = 0; i < 8; i++) ...for (int i = 0; i < 8; i++) ...
iconst 0
istore v0
iload v0
bipush 8
ificmpge +12
...
iinc v0, 1
goto -12
iconst 0
istore v0
iload v0
bipush 8
ificmpge +12
...
iinc v0, 1
goto -12
.class .dex
.java
Javac
Dx
const/4 v0, #0
const/16 v1, #8
if-ge v0, v1, 8
...
add-int/lit8 v0, v0, #1
goto -9
const/4 v0, #0
const/16 v1, #8
if-ge v0, v1, 8
...
add-int/lit8 v0, v0, #1
goto -9

14. Code representations
for (int i = 0; i < 8; i++) ...for (int i = 0; i < 8; i++) ...
iconst 0
istore v0
iload v0
bipush 8
ificmpge +12
...
iinc v0, 1
goto -12
iconst 0
istore v0
iload v0
bipush 8
ificmpge +12
...
iinc v0, 1
goto -12
.class .dex
.java
Javac
Efficient to store and execute
Inconvenient to process
Dx
const/4 v0, #0
const/16 v1, #8
if-ge v0, v1, 8
...
add-int/lit8 v0, v0, #1
goto -9
const/4 v0, #0
const/16 v1, #8
if-ge v0, v1, 8
...
add-int/lit8 v0, v0, #1
goto -9

15. LOCAL int n
FOR_STATEMENT:
- EXPRESSION_STATEMENT:
- ASG_OPERATION:
- LOCAL_REF i
- INT_LITERAL 0
- LT_OPERATION:
- LOCAL_REF i
- INT_LITERAL 8
- POSTFIX_INC_OPERATION:
- LOCAL_REF i
- ...
LOCAL int n
FOR_STATEMENT:
- EXPRESSION_STATEMENT:
- ASG_OPERATION:
- LOCAL_REF i
- INT_LITERAL 0
- LT_OPERATION:
- LOCAL_REF i
- INT_LITERAL 8
- POSTFIX_INC_OPERATION:
- LOCAL_REF i
- ...
Code representations
for (int i = 0; i < 8; i++) ...for (int i = 0; i < 8; i++) ...
iconst 0
istore v0
iload v0
bipush 8
ificmpge +12
...
iinc v0, 1
goto -12
iconst 0
istore v0
iload v0
bipush 8
ificmpge +12
...
iinc v0, 1
goto -12
.class .dex
.java
Javac
.jayce
Jack
const/4 v0, #0
const/16 v1, #8
if-ge v0, v1, 8
...
add-int/lit8 v0, v0, #1
goto -9
const/4 v0, #0
const/16 v1, #8
if-ge v0, v1, 8
...
add-int/lit8 v0, v0, #1
goto -9
Jill
Jack

16. Implications of Jack and Jill
● Java annotation processors – supported in Jack
E.g. Dagger, Butterknife
● Bytecode processors – only supported via Jill
E.g. JaCoCo, Retrolambda
● Other JVM languages – only supported via Jill
E.g. Scala, Groovy, Dart
● Instant Run – not supported yet

17. Implications of Jack and Jill
Libraries
(.jayce)
Jack
Assets
Compiled
XML resources
(.xml)
Aapt
Dalvik bytecode
(classes.dex)
Javac annotation processors
E.g. Dagger, Butterknife
Source code
(.scala,...)
Libraries
(.class)
XML resources
(.xml)
Assets
Runtime
(.class)
Jill
Jill Runtime
(.jayce)
Bytecode processors
Java bytecode
(.class)Scalac
Application
(.jayce)Jill

18. Internals
Jack: Java frontend
Eclipse ecj library
Jill: Java frontend
ASM4 library

19. Java 8: closures
.....
button.setOnClickListener(view -> .....);
.....
.....
button.setOnClickListener(view -> .....);
.....
.....
button.setOnClickListener(new MyActivity$LambdaImpl());
.....
.....
button.setOnClickListener(new MyActivity$LambdaImpl());
.....
public class MyActivity$LambdaImpl {
public void onClick(View view) {
.....
}
}
public class MyActivity$LambdaImpl {
public void onClick(View view) {
.....
}
}
Jack
For all versions
of Android

20. Device
More changes!
RunDalvik bytecode
(classes.dex)
Source code
(.java)
Libraries
(.class)
Runtime stubs
(.class)
Build Dalvik bytecode
(classes.oat)
Android
runtimeJack & Jill

21. OpenJDK
RunDalvik bytecode
(classes.dex)
Source code
(.java)
Libraries
(.class)
Build Dalvik bytecode
(classes.oat)
Android +
OpenJDK
runtime
Android +
OpenJDK
runtime stubs
(.class)
OpenJDK
Device
OpenJDK

22. Java 8: default methods
● In your own code:
● In the Android runtime:
public interface java.util.List<E> extends java.util.Collection<E> {
public abstract int size();
...
public default void sort(java.util.Comparator<? super E>) {
.....
}
}
public interface java.util.List<E> extends java.util.Collection<E> {
public abstract int size();
...
public default void sort(java.util.Comparator<? super E>) {
.....
}
}
public interface Foo {
public abstract void someMethod();
public void someDefaultMethod() {
....
}
}
public interface Foo {
public abstract void someMethod();
public void someDefaultMethod() {
....
}
}
Only on
Android N

23. New instructions
Dalvik bytecode
RunDalvik bytecode
(classes.dex)
Source code
(.java)
Libraries
(.class)
Build Dalvik bytecode
(classes.oat)
Android +
OpenJDK
runtime
Android +
OpenJDK
runtime stubs
(.class)
New instructions
Device

24. Java 8: closures
.....
● put-field-lambda
● get-field-lambda
● put-static-lambda
● get-static-lambda
● aget-lambda
● aput-lambda
● move-lambda
● cmp-lambda
● return-lambda
.....
● put-field-lambda
● get-field-lambda
● put-static-lambda
● get-static-lambda
● aget-lambda
● aput-lambda
● move-lambda
● cmp-lambda
● return-lambda Only on
Android N+
New Dalvik instructions:

25. Build performance
44s – Javac + dx (clean build)
1m9s – Javac + ProGuard optimize + dx (clean build)
24s – Javac + DexGuard (clean build)
2m36s – Javac + DexGuard optimize (clean build)
1m17s – Jack (clean build)
47s – Jack (clear all dex files)
15s – Javac + dx (clear all class files)15s – Javac + dx (clear all class files)
5s – Javac + dx (clear one class file)5s – Javac + dx (clear one class file)
2s – Javac + dx (code unchanged)2s – Javac + dx (code unchanged)
40s – Jack (clear one dex file)40s – Jack (clear one dex file)
3s – Jack (code unchanged)3s – Jack (code unchanged)
Google I/O app
(AMD A10-7800, Ubuntu 14.04, Java 8, Android Gradle 2.1.0 alpha1, Gradle daemon)
49s – Jack minify (clear all dex files)49s – Jack minify (clear all dex files)
21s – Javac + ProGuard + dx (clean build)21s – Javac + ProGuard + dx (clean build)

26. Application runtime performance
50,000 – Javac + dx
63,800 – Javac + ProGuard optimize + dx
82,300 – Javac + DexGuard optimize
54,500 – Jack
Caffeinemark benchmark
(Nexus 5, Android 6.0, ART)
+9%
+28%
+65%
(higher is better)

27. Application size
3.1M – Javac + dx
1.9M – Javac + ProGuard optimize + dx
1.8M – Javac + DexGuard optimize
1.9M – Jack + minify
Google I/O app
-39%
-38%
-44%
(smaller is better)

28. DexGuard
Java bytecode
(.class)
DexGuard
Libraries
(.class)
Javac
Optimized
assets
Optimized
XML resources
(.xml)
Aapt
Optimized
Dalvik bytecode
(classes.dex)
ProGuard
config
(.txt)
ProGuard
mapping
(.txt)
Source code
(.java)
Libraries
(.class)
XML resources
(.xml)
Assets
Android
runtime stubs
(.class)
Compiled
XML resources
(.xml)
Android
runtime stubs
(.class)
Assets
Native code
(.so)Clang
Source code
(.c / .cpp)
Optimized
native code
(.so)

29. Conclusions
● Huge changes
● Clean implementation
Internally

30. Conclusions
● Huge changes
● Clean implementation
● Different build process
● New intermediary representation
Internally
For languages and tools

31. Conclusions
● Huge changes
● Clean implementation
● More efficient builds
● Java 8
● Different build process
● New intermediary representation
Internally
For languages and tools
For app developers

32. Further reading
● “Experimental New Android Tool Chain - Jack and Jill”
http://tools.android.com/tech-docs/jackandjill
● “Java 8 Language Features”
https://developer.android.com/preview/j8-jack.html
● “Jack (Java Android Compiler Kit)”
https://source.android.com/source/jack.html
● AOSP repository
https://android.googlesource.com/toolchain/jack/
● “State of the ART”
http://androidbackstage.blogspot.com/2016/03/episode-45-state-of-art.html

33. Questions?
Size
Java bytecode
Performance
Jayce bytecode
Dalvik bytecode
Jack & Jill
ProGuard
DexGuard