After this talk, using plain old Java for Android development will no longer be good enough for you. You have been warned. Presented by Dino Kovač from Infinum.

1. We're an independent
design & development
agency.

2. infinum.co/android-sweets
Fresh news from Droid zone, curated by Željko Plesac

3. Benefits of using
Kotlin
DINO KOVAČ

4. BASIC INFO
• statically typed JVM language
• fully interoperable with Java
• developed by JetBrains

5. HISTORY
• in development since 2010
• stable version released at 15.2.2016.
• used in 10 projects internally at JetBrains

6. GOALS
• concise
• expressive
• toolable
• interoperable
• pragmatic

7. REAL EXAMPLES

8. MODELS

9. public static class LoginResponse {
@Json(name = "userName")
private String username;
@Json(name = "token_type")
private String bearer;
@Json(name = "expires_in")
private int expiresIn;
@Json(name = "access_token")
private String accessToken;
@Json(name = "refresh_token")
private String refreshToken;
public LoginResponse(String username, String bearer, int expiresIn, String accessToken, String refreshToken) {
this.username = username;
this.bearer = bearer;
this.expiresIn = expiresIn;
this.accessToken = accessToken;
this.refreshToken = refreshToken;
}
public String getUsername() {
return username;
}
public String getBearer() {
return bearer;
}
public int getExpiresIn() {
return expiresIn;
}
public String getAccessToken() {
return accessToken;
}
public String getRefreshToken() {
return refreshToken;
}
}

10. class LoginResponse(
@Json(name = "userName") val username: String,
@Json(name = "token_type") val bearer: String,
@Json(name = "expires_in") val expiresIn: Int,
@Json(name = "access_token") val accessToken: String,
@Json(name = "refresh_token") val refreshToken: String
)

11. KOTLIN ANDROID
EXTENSIONS

13. OPERATIONS WITH
COLLECTIONS

14. private List<FilterTagListView> tagGroupViews() {
List<FilterTagListView> filterTagListViews = new ArrayList<>();
for (int i = 0; i < filterContainer.getChildCount(); i++) {
View view = filterContainer.getChildAt(i);
if (view instanceof FilterTagListView) {
filterTagListViews.add((FilterTagListView) view);
}
}
return filterTagListViews;
}

15. private fun tagGroupViews(): List<FilterTagListView> {
return (0..filterContainer.childCount - 1)
.map { i -> filterContainer.getChildAt(i) }
.filter { childView -> childView is FilterTagListView }
.map { it as FilterTagListView }
}

16. /**
* finds view group which contains given tag and marks tag selected within that group
*/
public void addSelectedTag(CoupeTag tag) {
FilterTagListView view = null;
List<FilterTagListView> tagGroupViews = tagGroupViews();
for (FilterTagListView tagGroupView : tagGroupViews) {
if (tagGroupView.getFilter().getTitle().equals(tag.getFilter().getTitle())) {
view = tagGroupView;
break;
}
}
if (view != null) {
view.setTagSelection(tag.getTitle());
if (filtersSelectedListener != null) {
filtersSelectedListener.onSelected(getSelectedTags());
}
}
}

17. /**
* finds view group which contains given tag and marks tag selected within that group
*/
fun addSelectedTag(tag: CoupeTag) {
val view = tagGroupViews().firstOrNull { view ->
view.filter.title == tag.filter.title
}
view?.let {
view.setTagSelection(tag.title)
filterSelectedListener?.onSelected(getSelectedTags()?.toList())
}
}

18. LISTENER INTERFACES

19. // adapter
public interface OnCheckedChangeListener {
void onCheckedChange(Genre genre, boolean isChecked);
}
public void setOnCheckedChangeListener(@Nullable OnCheckedChangeListener listener) {
this.listener = listener;
}
if (listener != null) {
listener.onCheckedChange(genre, isChecked);
}
// activity
this.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChange(Genre genre, boolean isChecked) {
// TODO magic
}
});

20. // adapter
var onCheckedChangeListener: ((Genre, Boolean) -> Unit)? = null
onCheckedChangeListener?.invoke(genre, isChecked)
// activity
genresAdapter.onCheckedChangeListener = {
// TODO magic
}

21. CONVENIENCES

22. List<AirDate> dummyAirdates = new ArrayList<>();
dummyAirdates.add(new AirDate(ZonedDateTime.now(), 1));
dummyAirdates.add(new AirDate(ZonedDateTime.now().plusDays(1), 2));
dummyAirdates.add(new AirDate(ZonedDateTime.now().plusWeeks(1), 3));

23. val dummyAirDates = listOf(
AirDate(ZonedDateTime.now(), 1),
AirDate(ZonedDateTime.now().plusDays(1), 2),
AirDate(ZonedDateTime.now().plusWeeks(1), 3)
)

24. OTHERS
• setOf(), mapOf(), arrayOf()
• emptyList(), emptySet(), emptyMap(),
emptyArray()
• … plenty more

25. RISKS

26. WHAT IF JET BRAINS GOES
OUT OF BUSINESS?

27. JETBRAINS
• 500+ employees
• fully bootstrapped
• steady revenue stream (subscription model)
• heavily invested in Kotlin

28. LANGUAGE STABILITY

29. SWIFT
OPEN SOURCE

31. I think it is fair to say that "open design" is slower
and less predictable than "closed design”.
However, the end result is significantly better, and
therefore the tradeoff is worth it.
- CHRIS LATTNER, APPLE

32. WHAT IF GOOGLE BREAKS
COMPATIBILITY?

33. Kotlin is interesting: works well with Java, more
concise. JetBrains has done a nice job supporting
this on android. But no plans to officially support
anything new.
- ANWAR, ANDROIDENGTEAM

34. I don’t think we have any plans to break what
already works there, but we don’t have plans to
have a second, idiomatic-Kotlin version of the
whole framework API surface area either.
- ADAM, ANDROIDENGTEAM

35. We don’t have any plans to move to a new
language. Java has a lot of advantages to it and the
versions 8, 9, and 10 have some pretty interesting
stuff for developers.
- ANWAR, ANDROIDENGTEAM

36. CONCLUSION
• Kotlin can help you be more productive
• Kotlin is here to stay
• Be aware of the risks!

37. Thank you!
DINO@INFINUM.CO
@DINO_BLACKSMITH
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