Kotlin is a programming language that the author chose to use for Android development. Some reasons for this choice include curiosity about the language, reviews of its code from JetBrains, and benefits like small app size and fast compilation. While there was a learning curve of around 50 hours, the syntax and approach are different from Java. Some of the features the author most appreciates about Kotlin are its safe code, simple class definitions, lambda expressions, and string templates. Issues are addressed quickly by JetBrains and the Kotlin team. Recommendations for learning Kotlin include reviewing documentation on the Kotlin website and Google samples. Major companies that use Kotlin include Google and JetBrains.

1. KOTLIN
MOJE DOŚWIADCZENIE

2. DAMIAN PETLA
ANDROID DEVELOPER
e-mail: damian.petla@schibsted.pl
LinkedIn: pl.linkedin.com/in/damianpetla

4. 1. DLACZEGO WYBRAŁEM
KOTLINA?
CIEKAWOŚĆ
CODE REVIEW Z iOS
JETBRAINS - ZNANA MARKA
ROZMIAR APK I SZYBKA KOMPILACJA

5. 2. CZY TRUDNO JEST
ZACZĄĆ?
50 GODZIN
SKŁADNIA
NOWE PODEJŚCIE

6. class User(val name: String, age: Int?)
val name: String = “Damian”
var isSuperUser: Boolean = true
var pet: String? = null
public fun sayHi(name: String, times: Int = 3) {
for (i in 1..times) {
println(“Hi $name”)
}
}
private fun getSome() : String {
return “some”
}
Kotlin

7. 3. CO NAJBARDZIEJ MI SIĘ
PODOBA W KOTLINIE?
BEZPIECZNY KOD

8. InputStream stream = ...
if (stream != null) {
stream.close();
}
stream.close()
stream?.close()
Java
Kotlin

9. 3. CO NAJBARDZIEJ MI SIĘ
PODOBA W KOTLINIE?
BEZPIECZNY KOD
PROSTE DEFINICJE KLAS

10. public class Item {
private String type;
public Item(String type) {
this.type = type;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Item item2 = (Item) o;
if (type != null ? !type.equals(item2.type) : item2.type != null) return false;
return true;
}
@Override
public int hashCode() {
return type != null ? type.hashCode() : 0;
}
@Override
public String toString() {
return "Item2{" +
"type='" + type + ''' +
'}';
}
}
public class Article extends Item {
private Boolean isDeleted;
private String id;
private String category;
private String published;
private String publishedFormatted;
private String firstPublished;
private String updated;
private String created;
private List<Topic> topics;
private String title;
private String newsLifetime;
private Integer newsValue;
private List<Author> authors;
private List<Resource> resources
private Version version;
private String vignette;
private String displaySize;
private Boolean live;
private Boolean breaking;
private Story story;
private Boolean sponsored = false;
public Article(String type) {
super(type);
}
public Article(String type, Boolean isDeleted, String id, String category, String published,
String publishedFormatted, String firstPublished, String updated, String created,
List<Topic> topics, String title, String newsLifetime, Integer newsValue,
List<Author> authors, List<Resource> resources, Version version, String vignette,
String displaySize, Boolean live, Boolean breaking, Story story, Boolean sponsored) {
super(type);
this.isDeleted = isDeleted;
this.id = id;
this.category = category;
this.published = published;
this.publishedFormatted = publishedFormatted;
this.firstPublished = firstPublished;
this.updated = updated;
this.created = created;
this.topics = topics;
this.title = title;
this.newsLifetime = newsLifetime;
this.newsValue = newsValue;
this.authors = authors;
this.resources = resources;
this.version = version;
this.vignette = vignette;
this.displaySize = displaySize;
this.live = live;
this.breaking = breaking;
this.story = story;
this.sponsored = sponsored;
}
public Boolean getIsDeleted() {
return isDeleted;
}
public void setIsDeleted(Boolean isDeleted) {
this.isDeleted = isDeleted;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getCategory() {
return category;
}
public void setCategory(String category) {
this.category = category;
}
public String getPublished() {
return published;
}
public void setPublished(String published) {
this.published = published;
}
public String getPublishedFormatted() {
return publishedFormatted;
}
public void setPublishedFormatted(String publishedFormatted) {
this.publishedFormatted = publishedFormatted;
}
public String getFirstPublished() {
return firstPublished;
}
public void setFirstPublished(String firstPublished) {
this.firstPublished = firstPublished;
}
public String getUpdated() {
return updated;
}
public void setUpdated(String updated) {
this.updated = updated;
}
public String getCreated() {
return created;
}
public void setCreated(String created) {
this.created = created;
}
public List<Topic> getTopics() {
return topics;
}
public void setTopics(List<Topic> topics) {
this.topics = topics;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getNewsLifetime() {
return newsLifetime;
}
public void setNewsLifetime(String newsLifetime) {
this.newsLifetime = newsLifetime;
}
public Integer getNewsValue() {
return newsValue;
}
public void setNewsValue(Integer newsValue) {
this.newsValue = newsValue;
}
public List<Author> getAuthors() {
return authors;
}
public void setAuthors(List<Author> authors) {
this.authors = authors;
}
public List<Resource> getResources() {
return resources;
}
public void setResources(List<Resource> resources) {
this.resources = resources;
}
public Version getVersion() {
return version;
}
public void setVersion(Version version) {
this.version = version;
}
public String getVignette() {
return vignette;
}
public void setVignette(String vignette) {
this.vignette = vignette;
}
public String getDisplaySize() {
return displaySize;
}
public void setDisplaySize(String displaySize) {
this.displaySize = displaySize;
}
public Boolean getLive() {
return live;
}
public void setLive(Boolean live) {
this.live = live;
}
public Boolean getBreaking() {
return breaking;
}
public void setBreaking(Boolean breaking) {
this.breaking = breaking;
}
public Story getStory() {
return story;
}
public void setStory(Story story) {
this.story = story;
}
public Boolean getSponsored() {
return sponsored;
}
public void setSponsored(Boolean sponsored) {
this.sponsored = sponsored;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
if (!super.equals(o)) return false;
Article article2 = (Article) o;
if (authors != null ? !authors.equals(article2.authors) : article2.authors != null) return false;
if (breaking != null ? !breaking.equals(article2.breaking) : article2.breaking != null) return false;
if (category != null ? !category.equals(article2.category) : article2.category != null) return false;
if (created != null ? !created.equals(article2.created) : article2.created != null) return false;
if (displaySize != null ? !displaySize.equals(article2.displaySize) : article2.displaySize != null)
return false;
if (firstPublished != null ? !firstPublished.equals(article2.firstPublished) : article2.firstPublished != null)
return false;
if (id != null ? !id.equals(article2.id) : article2.id != null) return false;
if (isDeleted != null ? !isDeleted.equals(article2.isDeleted) : article2.isDeleted != null) return false;
if (live != null ? !live.equals(article2.live) : article2.live != null) return false;
if (newsLifetime != null ? !newsLifetime.equals(article2.newsLifetime) : article2.newsLifetime != null)
return false;
if (newsValue != null ? !newsValue.equals(article2.newsValue) : article2.newsValue != null) return false;
if (published != null ? !published.equals(article2.published) : article2.published != null) return false;
if (publishedFormatted != null ? !publishedFormatted.equals(article2.publishedFormatted) :
article2.publishedFormatted != null) return false;
if (resources != null ? !resources.equals(article2.resources) : article2.resources != null) return false;
if (sponsored != null ? !sponsored.equals(article2.sponsored) : article2.sponsored != null) return false;
if (story != null ? !story.equals(article2.story) : article2.story != null) return false;
if (title != null ? !title.equals(article2.title) : article2.title != null) return false;
if (topics != null ? !topics.equals(article2.topics) : article2.topics != null) return false;
if (updated != null ? !updated.equals(article2.updated) : article2.updated != null) return false;
if (version != null ? !version.equals(article2.version) : article2.version != null) return false;
if (vignette != null ? !vignette.equals(article2.vignette) : article2.vignette != null) return false;
return true;
}
@Override
public int hashCode() {
int result = super.hashCode();
result = 31 * result + (isDeleted != null ? isDeleted.hashCode() : 0);
result = 31 * result + (id != null ? id.hashCode() : 0);
result = 31 * result + (category != null ? category.hashCode() : 0);
result = 31 * result + (published != null ? published.hashCode() : 0);
result = 31 * result + (publishedFormatted != null ? publishedFormatted.hashCode() : 0);
result = 31 * result + (firstPublished != null ? firstPublished.hashCode() : 0);
result = 31 * result + (updated != null ? updated.hashCode() : 0);
result = 31 * result + (created != null ? created.hashCode() : 0);
result = 31 * result + (topics != null ? topics.hashCode() : 0);
result = 31 * result + (title != null ? title.hashCode() : 0);
result = 31 * result + (newsLifetime != null ? newsLifetime.hashCode() : 0);
result = 31 * result + (newsValue != null ? newsValue.hashCode() : 0);
result = 31 * result + (authors != null ? authors.hashCode() : 0);
result = 31 * result + (resources != null ? resources.hashCode() : 0);
result = 31 * result + (version != null ? version.hashCode() : 0);
result = 31 * result + (vignette != null ? vignette.hashCode() : 0);
result = 31 * result + (displaySize != null ? displaySize.hashCode() : 0);
result = 31 * result + (live != null ? live.hashCode() : 0);
result = 31 * result + (breaking != null ? breaking.hashCode() : 0);
result = 31 * result + (story != null ? story.hashCode() : 0);
result = 31 * result + (sponsored != null ? sponsored.hashCode() : 0);
return result;
}
@Override
public String toString() {
return "Article{" +
open class Item(val type: ItemTypeEnum): Serializable
data class Article(type: ItemTypeEnum,
val isDeleted: Boolean?,
val id: String,
val category: String,
val published: String,
var publishedFormatted: String?,
val firstPublished: String?,
val updated: String,
val created: String,
val topics: Array<Topic>,
val title: String,
val newsLifetime: String,
val newsValue: Int,
val authors: Array<Author>,
val resources: Array<Resource>,
val version: Version?,
val vignette: String?,
val displaySize: String,
val live: Boolean?,
val breaking: Boolean?,
val story: Story?,
val sponsored: Boolean = false
) : Item(type)
Java - 354 Kotlin - 25

11. data class User(val name: String,
val surname: String,
val age: Int)
val user = User(“Damian”, “Petla”, 33)
val user2 = user.copy(age = 30, name = “Adam”)
println(user)
println(user2)
User(name=Damian, surname=Petla, age=33)
User(name=Adam, surname=Petla, age=30)
Kotlin
Log

12. 3. CO NAJBARDZIEJ MI SIĘ
PODOBA W KOTLINIE?
BEZPIECZNY KOD
PROSTE DEFINICJE KLAS
LAMBDA
STRING TEMPLATES

13. Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
System.out.println(“Hello! " + v.isOpaque());
}
});
Java
Kotlin
val button = findViewById(R.id.button) as Button
button.setOnClickListener { println("Hello! ${it.isOpaque()}") }

14. 3. CO NAJBARDZIEJ MI SIĘ
PODOBA W KOTLINIE?
BEZPIECZNY KOD
PROSTE DEFINICJE KLAS
LAMBDA
STRING TEMPLATES
SMART CAST

15. int l = 0;
if (obj instanceof String) {
l = ((String)obj).length;
}
Java
Kotlin
var l = 0
if (obj is String) {
l = obj.length
}
val l : Int = (obj as? String)?.length ?: 0

16. 3. CO NAJBARDZIEJ MI SIĘ
PODOBA W KOTLINIE?
BEZPIECZNY KOD
PROSTE DEFINICJE KLAS
LAMBDA
STRING TEMPLATES
SMART CAST
FUNCTION EXTENSIONS

17. String utcDate = ...
String formatted = Utilites.toPrettyDate(utcDate);
textView.setText(formatted);
Java
Kotlin
textView.setText(utcDate.toPrettyDate())
fun String.toPrettyDate(): String {
return “$this is formatted now”
}

18. 4. CZY SĄ JAKIEŚ
PROBLEMY Z KOTLINEM?
SZYBKA ODPOWIEDŹ NA ZGŁOSZONE BŁEDY
JETBRAINS AKTYWNY NA STACK OVERFLOW
220 BUGÓW NAPRAWIONYCH W WERSJI M11(0.11.91)

20. Experimental J-Unit support

21. Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP
Java
Kotlin
Build.VERSION.SDK_INT >= 21

22. 5. OD CZEGO ZACZĄĆ
NAUKĘ?

23. HTTP://KOTLINLANG.ORG/DOCS/REFERENCE/

24. HTTP://KOTLINLANG.ORG/DOCS/TUTORIALS/KOTLIN-ANDROID.HTML

25. HTTPS://DOCS.GOOGLE.COM/DOCUMENT/D/1RES3EP-HJXWA8KZI0YQDBEHCQTT29HG8P44AA9W0DM8

26. 6. KTO UŻYWA KOTLINA?

27. 7. CZY MAM JAKIEŚ PORADY
NA POCZĄTEK?
!! ZAMIAST ?
CZĘSTO WRACAJ DO DOKUMENTACJI
UDZIELAJ SIĘ W COMMUNITY

28. Q & A

29. EXTRA
Android Kotlin Plugin