Introduction to Kotlin, Pt. 1

Internal talk given to the Android team at BAM Tech.

Transcript

1. Introduction to Kotlin, Part 1 Introduction to Kotlin Pt. 1, Richard Cirerol
2. Is Kotlin a hipster language? Introduction to Kotlin Pt. 1, Richard Cirerol
3. Is Kotlin a hipster language? Introduction to Kotlin Pt. 1, Richard Cirerol
4. Why Kotlin? • Concise • Expressive • Java-interoperable • Easy to integrate Introduction to Kotlin Pt. 1, Richard Cirerol
5. Is Java 6 that bad?1 1 "Advancing Android Development with Kotlin", Jake Wharton Introduction to Kotlin Pt. 1, Richard Cirerol
6. Problem: Date and Calendar APIs1 • Use JodaTime or ThreeTenBP 1 "Advancing Android Development with Kotlin", Jake Wharton Introduction to Kotlin Pt. 1, Richard Cirerol
7. Problem: Lack of Java 8 Streams1 List<String> list = people.stream() .map(Person::getName).collect(Collectors.toList()); 1 "Advancing Android Development with Kotlin", Jake Wharton Introduction to Kotlin Pt. 1, Richard Cirerol
8. Problem: Lack of Java 8 Streams1 • Use Guava Collections • Use Apache Collections • Use RxJava (with Retrolambda) List<String> list = Observable.from(people) .map(Person::getName).toBlocking().toList() 1 "Advancing Android Development with Kotlin", Jake Wharton Introduction to Kotlin Pt. 1, Richard Cirerol
9. Problem: Lack of Lambdas1 • Use Retrolambda 1 "Advancing Android Development with Kotlin", Jake Wharton Introduction to Kotlin Pt. 1, Richard Cirerol
10. Problem: Lack of extension methods1 • Use utility classes 1 "Advancing Android Development with Kotlin", Jake Wharton Introduction to Kotlin Pt. 1, Richard Cirerol
11. Problem: NullPointerException1 The "billion-dollar" mistake • Null guard wrappers 1 "Advancing Android Development with Kotlin", Jake Wharton Introduction to Kotlin Pt. 1, Richard Cirerol
12. Problem: Java has the unique ability to make even the easiest possible statement so very tedious and VERBOSE.1 • For anonymous classes, use Retrolambda instead • Otherwise, you're SOL 1 "Advancing Android Development with Kotlin", Jake Wharton Introduction to Kotlin Pt. 1, Richard Cirerol
13. Why Kotlin? Statically typed programming language for the JVM, Android and the browser 100% interoperable with Java™ -- JetBrains Introduction to Kotlin Pt. 1, Richard Cirerol
14. Why Kotlin? Think of Kotlin as C# for the JVM, Scala the Good Parts, Java++ or simply a decent general purpose language that won't require the blood of your first born. -- James Hughes (https://yobriefca.se/blog/2016/02/24/ kotlin-2-years-on/) Introduction to Kotlin Pt. 1, Richard Cirerol
15. Other JVM options: • Scala • Xtend • Clojure • Ceylon • Groovy Introduction to Kotlin Pt. 1, Richard Cirerol
16. Isn't Kotlin really new? Yes and no. • First commit was in November 2010 • v1.0 RTW in February 2016 • 1.0.3 is current stable • 1.0.4 is in EAP • Additional updates for performance, tooling, bug fixes Introduction to Kotlin Pt. 1, Richard Cirerol
17. Isn't Kotlin really new? ...and yes. • v1.1 is in development • Backwards-compatible • Focus on using Java 8 features Introduction to Kotlin Pt. 1, Richard Cirerol
18. What are the chances that it will go away soon? Not likely. • JetBrains is building its products on Kotlin • JetBrains is not building Kotlin as a revenue source • Kotlin is open-source (125+ contributors, including 20+ from JetBrains) Introduction to Kotlin Pt. 1, Richard Cirerol
19. Isn't it hard to learn? • Has C roots • Similar to Java and C# • Very similar to Swift • In no way similar to Objective-C ! Introduction to Kotlin Pt. 1, Richard Cirerol
20. Let's revisit the Java 6 Problems Introduction to Kotlin Pt. 1, Richard Cirerol
21. Java 6 Problem: Date and Calendar APIs • Same solution - use JodaTime or ThreeTenBP • v1.1 will likely expose java.time Introduction to Kotlin Pt. 1, Richard Cirerol
22. Java 6 Problem: Lack of Java 8 Streams • Part of the standard library // Java 8 stream/collect List<String> list = people.stream() .map(Person::getName).collect(Collectors.toList()); // Kotlin val list = people.map { it.name } Introduction to Kotlin Pt. 1, Richard Cirerol
23. Java 6 Problem: Lack of Lambdas • Part of the standard library // Java 8 stream/collect List<String> list = people.stream() .map(Person::getName).collect(Collectors.toList()); // Kotlin val list = people.map { it.name } //OR val list = people.map { person -> person.name } Introduction to Kotlin Pt. 1, Richard Cirerol
24. Java 6 Problem: Lack of extension methods • Part of the standard library fun String.ellipsize(size: Int): String { return "${this.substring(0, size)}..." } "Hello, Kotlin".ellipsize(5) // Hello... Introduction to Kotlin Pt. 1, Richard Cirerol
25. Java 6 Problem: NPE // compiler exception val name: String = null // Must make type nullable val name: String? = null // compiler exception, name can be null now, cannot call length // length type is inferred val length = name.length // Inline check for null, name?.length evaluates to `null` if name==null // Provide alternative using Elvis operator val length = name?.length ?: 0 // Can force compiler to assume not null using double-bang // Possible NPE at runtime (but this is your own fault) val length = name!!.length Introduction to Kotlin Pt. 1, Richard Cirerol
26. Java 6 Problem: Verbosity public class Person { private String firstName; private String lastName; private String email; public Person(final String firstName, final String lastName, final String email) { this.firstName = firstName; this.lastName = lastName; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(final String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(final String lastName) { this.lastName = lastName; } public String getEmail() { return email; } public void setEmail(final String email) { this.email = email; } @Override public boolean equals(final Object o) { if (this == o) return true; if (!(o instanceof Person)) return false; final Person person = (Person) o; if (firstName != null ? !firstName.equals(person.firstName) : person.firstName != null) return false; if (lastName != null ? !lastName.equals(person.lastName) : person.lastName != null) return false; return email != null ? email.equals(person.email) : person.email == null; } @Override public int hashCode() { int result = firstName != null ? firstName.hashCode() : 0; result = 31 * result + (lastName != null ? lastName.hashCode() : 0); result = 31 * result + (email != null ? email.hashCode() : 0); return result; } @Override public String toString() { return "Person{" + "firstName='" + firstName + '\'' + ", lastName='" + lastName + '\'' + ", email='" + email + '\'' + '}'; } } Introduction to Kotlin Pt. 1, Richard Cirerol
27. Java 6 Problem: Verbosity class Customer(val firstName: String, val lastName: String, val email: String) // no hashcode(), equals(), or toString() Introduction to Kotlin Pt. 1, Richard Cirerol
28. Java 6 Problem: Verbosity data class Customer(val firstName: String, val lastName: String, val email: String) // has hashcode(), equals(), and toString() // v1.0 cannot subclass, v1.1 can subclass Introduction to Kotlin Pt. 1, Richard Cirerol
29. The Language Introduction to Kotlin Pt. 1, Richard Cirerol
30. The Language: Classes //java public class Foo { } //kotlin class Foo Introduction to Kotlin Pt. 1, Richard Cirerol
31. The Language: Classes //java public final class Foo { private Bar bar; public Foo(@NotNull Bar bar){ this.bar = bar; } } //kotlin class Foo(var bar: Bar) Introduction to Kotlin Pt. 1, Richard Cirerol
32. The Language: Classes //java public final class Foo { private final Bar bar; public Foo(@NotNull Bar bar){ this.bar = bar; } } //kotlin class Foo(val bar: Bar) Introduction to Kotlin Pt. 1, Richard Cirerol
33. The Language: Classes //java public final class Foo { private final Bar bar; private final String baz; public Foo(@NotNull Bar bar){ this(bar, "baz") } public Foo(@NotNull Bar bar, @NotNull String baz){ this.bar = bar; this.baz = baz; } } //kotlin class Foo(val bar:Bar, val baz:String = "baz") Introduction to Kotlin Pt. 1, Richard Cirerol
34. The Language: Classes //java public final class Foo { private final Bar bar; private final String baz; public Foo(@NotNull Bar bar){ this(bar, "baz") } public Foo(@NotNull Bar bar, @NotNull String baz){ this.bar = bar; this.baz = baz; } } //kotlin @JvmOverloads class Foo(val bar:Bar, val baz:String = "baz") Introduction to Kotlin Pt. 1, Richard Cirerol
35. The Language: Methods //java public void doSomething() { // do something } //kotlin fun doSomething(): Unit { // do something } Introduction to Kotlin Pt. 1, Richard Cirerol
36. The Language: Methods //java public void doSomething() { // do something } //kotlin fun doSomething() { // do something } Introduction to Kotlin Pt. 1, Richard Cirerol
37. The Language: Methods //java void doSomething() { // do something } //kotlin internal fun doSomething() { // do something } Introduction to Kotlin Pt. 1, Richard Cirerol
38. The Language: Methods //java private void doSomething() { // do something } //kotlin private fun doSomething() { // do something } Introduction to Kotlin Pt. 1, Richard Cirerol
39. The Language: Methods //java public int getNumber() { return 0; } //kotlin fun getNumber(): Int { return 0 } Introduction to Kotlin Pt. 1, Richard Cirerol
40. The Language: Methods //java public int getNumber() { return 0; } //kotlin fun getNumber() = 0 Introduction to Kotlin Pt. 1, Richard Cirerol
41. The Language: Anonymous Methods Click-listener Example2 //java public interface OnClickListener { void onClick(View v); } view.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { doSomething("Click"); } }); 2 http://antonioleiva.com/functional-programming-android-kotlin-lambdas/ Introduction to Kotlin Pt. 1, Richard Cirerol
42. The Language: Anonymous Methods Click-listener Example2 //kotlin view.setOnClickListener(object : OnClickListener { override fun onClick(v: View) { doSomething("Click") } }) 2 http://antonioleiva.com/functional-programming-android-kotlin-lambdas/ Introduction to Kotlin Pt. 1, Richard Cirerol
43. The Language: Anonymous Methods Click-listener Example2 //kotlin view.setOnClickListener({ view -> doSomething("Click") }) view.setOnClickListener({ doSomething("Click") }) view.setOnClickListener(){ doSomething("Click") } view.setOnClickListener { doSomething("Click")} 2 http://antonioleiva.com/functional-programming-android-kotlin-lambdas/ Introduction to Kotlin Pt. 1, Richard Cirerol
44. To be continued... Introduction to Kotlin Pt. 1, Richard Cirerol