This document summarizes different programming language options for Android development and discusses their advantages and disadvantages. It focuses on Scala, noting that while it is statically typed, compiles to Java bytecode, and allows access to all Android classes, performance can sometimes be slow. It provides examples of how to use Scala features like type inference, imports, lazy vals, mixins, collections, functions, pattern matching, implicits, and XML processing. It also cautions that performance sensitive parts may require removing features like for-comprehensions and avoiding boxed types.

1. Scala on Android

2. Android Development
● Write lots of Java code
● Write UI and other resources in XML
● Generate Java code from resources
● Compile Java code into “.class” files
● Run proguard
● Compile class files to Dalvik Executable (DEX)
● Deploy on device

3. Dalvik VM
● Does not support “.class” bytecode format
● Can not use libraries which generate bytecode
● Devices have limited CPU and Memory
● Can not easily share libraries between
applications

4. Eclipse
● Has nice UI editors
● IDE is a build tool

5. Alternative Languages for Android

6. Jython
● Does not have enough community support
● Slow
● Dynamic

7. JRuby
● Ruboto framework
● Dynamic
● Need to use java code generation

8. Clojure
● Very cool :)
● Very slow start-up time
● Sometimes need to generate bytecode

9. PHP
Who cares?

10. Rhino
● Nice language
● Can run with optimization turned off
● Completely interpreted
● Dynamic

11. Groovy
???

12. Scala
● Statically typed
● Compiled to Java bytecode
● Has access to all classes in Android
● Fast
● but sometimes slow :)
● Has SBT
● Android
● Maven artifacts

13. How to build Scala apps for Android
● ANT
● Maven
● SBT + Android Plugin

14. Little nice things about Scala

15. Type Inference
● Improve readability
● Reduce number of imports
● Less typing

16. val stream = getAssets().open("areas.json")
val stream: InputStream =
getAssets().open("areas.json")

17. Import statement
import android.view.{
Window, Menu, MenuItem, KeyEvent, View
}
import android.util.Log.{e => error}

18. Lazy vals
lazy val searchBox =
findViewById(R.id.searchBox)
.asInstanceOf[AutoCompleteTextView]

19. Mixin Inheritance
class MainActivity extends MapActivity
with Logging
with DatabaseHelpers
with MapHelpers

20. Collections
● Best collection library I ever used
● Sorry google-collections...
● Using arrays is easy
● @specialized

21. Collection examples
val suggestions = areas map { _.name }
val index = areas.indexWhere(
_.name == searchString
)
val index =
areas.indexWhere(_.contains(coordinate))
pointList.minBy(_.lat)

22. First class functions
class AreaOverlay(
areas: Array[Area],
selectListener: Int => Unit
)
new AreaOverlay(
areas, this.onAreaSelected
)

23. Convert listeners into functions
implicit def fn2ClickListener(
f: View => Unit
): View.OnClickListener =
new View.OnClickListener() {
override def onClick(v: View) = f(view)
}
exitButton.setOnClickListener(
this.onExitClick
)

24. Files
● Directory structure is not forced to mirror
packages
● Files can contain any amount of classes

25. Pattern matching
● No NPEs when using Option[T]
● Easy to work with data objects

26. Pattern matching
lastLocation match {
case Some(c@Coordinate(lat, lon)) =>
...
case None =>
...
}

27. Implicits
implicit def coordinate2geopoint(
c: Coordinate
): GeoPoint = new GeoPoint(
c.lat * 1.0e6 toInt, c.lon * 1.0e6 toInt
)

28. XML
for (s <- xml "Document" "Style")
placemarkElem "Polygon"
"outerBoundaryIs" "LinearRing"
"coordinates"

29. Bad stuff
● Performance sensitive parts
● Learn to use “javap”
● Remove for-comprehensions and lambda functions
● Do not use boxed types “by accident”
● Tools
● UI Editor
● Debugger
● Build time (dex'ing of scala library)

30. What I missed from Java
● Google Guice
● Maven
● Good Eclipse integration
● Feeling important...

31. Thank you!

32. Questions?