The document discusses features of a statically typed programming language that runs on the JVM, Android, and the browser, emphasizing interoperability with Java. It includes code snippets demonstrating payment processing, string handling, and UI interactions in both Java and Kotlin. Additionally, it covers collections, extension functions, and data classes in Kotlin.

4. Statically typed programming language
for the JVM, Android and the browser
100% interoperable with Java™

12. PaymentRobot payment = new PaymentRobot();
ResultRobot result = payment
.amount(42_00)
.recipient("foo@bar.com")
.send();
result.isSuccess();

13. val payment = PaymentRobot()
val result = payment
.amount(4200)
.recipient("foo@bar.com")
.send()
result.isSuccess()

14. val result = payment {
amount(4200)
recipient("foo@bar.com")
}.send()
result.isSuccess()

15. payment {
amount(4200)
recipient("foo@bar.com")
}.send {
isSuccess()
}

16. payment {
amount(4200)
recipient("foo@bar.com")
} send {
isSuccess()
}

17. payment {
amount(4200)
recipient("foo@bar.com")
send()
}
birthday {
date(1970, 1, 1)
next()
}
ssn {
value("123-56-7890")
next()
}
result {
isSuccess()
}

24. public String foo() {
...
}
// null or non-null?
String f = foo();

25. @NonNull
public String foo() {
...
}
// non-null
String f = foo();

26. // nullable
fun nullable(): String? {
...
}
// non-null
fun nonNull(): String {
...
}

27. // ok
val foo: String? = "foo"
// compile error
val bar: String = null

28. String foo = "foo";
String bar = "foo";
// isEquals: true
boolean isEquals = foo.equals(bar);

29. String foo = "foo";
String bar = "foo";
// isEquals: false
boolean isEquals = foo == bar;

30. val foo = "foo"
val bar = "bar"
// isEquals: true
val isEquals = foo == bar

32. // MyFunctions.kt
package com.sample.package
fun foo() { }

33. // OtherFunctions.kt
package com.sample.package.others
// import function foo()
import com.sample.package.foo
fun baz() {
foo()
}

36. public class MainActivity extends AppCompatActivity {
Button btnCalligraphy;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnCalligraphy = (Button) findViewById(R.id.btn_calligraphy);
btnCalligraphy.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
// Do something
}
});
}
}

37. class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
btn_calligraphy.setOnClickListener {
// Do something
}
}
}

38. view.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(
v.getContext().getApplicationContext(),
"Hello", Toast.LENGTH_SHORT).show();
}
});

39. view.setOnClickListener({ v ->
Toast.makeText(v.context.applicationContext,
"Hello", Toast.LENGTH_SHORT).show()
})

40. view.setOnClickListener { v ->
Toast.makeText(v.context.applicationContext,
"Hello", Toast.LENGTH_SHORT).show()
}

41. view.setOnClickListener {
Toast.makeText(it.context.applicationContext,
"Hello", Toast.LENGTH_SHORT).show()
}

42. val people : List<String> = ..
people.filter { it.startsWith('S') }
.filter { it.length < 10 }
.onEach { it.toUpperCase() }
.forEach { println(it) }

43. val people : List<String> = ..
people.filter { it.startsWith('S') }
.filter { it.length < 10 }
.onEach(String::toUpperCase)
.forEach(::println)

44. val people : List<String> = ..
people.stream()
.filter { it.startsWith('S') }
.filter { it.length < 10 }
.map(String::toUpperCase)
.forEach(::println)

45. var foo : String = "Foo"
foo = "FOO"
val bar : String = "Bar"
bar = "BAR"

46. var foo : String = "Foo"
foo = "FOO"
val bar : String = "Bar"
bar = "BAR"
Compile Error (val cannot be reassigned)

47. val mutableList : MutableList<String>
= mutableListOf(“foo", "bar", "baz")
mutableList.add("fizz")
val immutableList : List<String>
= listOf("foo", "bar", "baz")
immutableList.add("fizz")

48. val mutableList : MutableList<String>
= mutableListOf("foo", "bar", "baz")
mutableList.add("fizz")
val immutableList : List<String>
= listOf("foo", "bar", "baz")
immutableList.add("fizz")
Compile Error (val cannot be reassigned)

51. val emptyStringList = listOf<String>()
val cities = listOf("Seoul", "Busan")
val mutableCities = mutableListOf("Seoul, Busan")

52. val emptyStringSet = setOf<String>()
val cities = setOf("Seoul", "Busan")
val mutableCities = mutableSetOf("Seoul, Busan")

53. val pair : Pair<String, String> = Pair("Seoul", "서울")

54. val pair : Pair<String, String> = "Seoul" to "서울"

55. public class Person {
String name;
String address;
Person(String name, String address) {
this.name = name;
this.address = address;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}

56. public class Person {
String name;
String address;
Person(String name, String address) {
this.name = name;
this.address = address;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Person person = (Person) o;
if (!name.equals(person.name)) {
return false;
}
return address != null ? address.equals(person.address) : person.address == null;
}
@Override
public int hashCode() {
int result = name.hashCode();
result = 31 * result + (address != null ? address.hashCode() : 0);
return result;
}
@Override

57. data class Person(val name: String, val address: String)

58. Toast.makeText(applicationContext,
"Hello, Kotlin!", Toast.LENGTH_SHORT).show()

59. // Define an extension function on Context
fun Context.toast(message: String) {
Toast.makeText(this.applicationContext,
message, Toast.LENGTH_SHORT).show()
}
// available in class Context and its descendants
toast("Hello, Kotlin!")

64. Happy Kotlin!