레진코믹스 안드로이드 앱은 왜 코틀린을 쓰게 된 것일까요? 그 이유와 함께, 코틀린을 도입하면서 겪은 경험담과 팁을 공유합니다. Kotlin Night Seoul 2017 2017.4.12

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!