Kotlin: Let's Make Android Great Again

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

MyActivity.java
btnDoIt = (Button) findViewById(R.id.btn_do_it);

MyActivity.java
btnDoIt = (Button) findViewById(R.id.btn_do_it);
btnDoIt.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO
}
});

WithRxJava.java
Observable.fromArray(1, 2, 3, 4, 5)
.map(new Function<Integer, String>() {
@Override
public String apply(Integer param) {
return "A" + param;
}
});

WithRxJava.java
Observable.fromArray("1", "2", "3", "4", "5")
.map(new Function<Integer, String>() {
@Override
public String apply(Integer param) {
return "A" + param;
}
});

WithRxJava.java
Observable.fromArray("1", "2", "3", "4", "5")
.map(new Function<String, String>() {
@Override
public String apply(String param) {
return "A" + param;
}
});

User.java
String getAddress() {
...
}
User user = getCurrentUser();
user.getAddress().toUpperCase();

Extended
Seoul
I call it my billion-dollar mistake. This has
led to innumerable errors … probably
caused a billion dollars of pain and damage
in the last forty years.
Extended
Seoul
- Tony Hoare

User.java
return this.address;
}

User.java
return null == this.address ? "" : this.address;
}

User.java
@Nullable
return this.address;
}

User.java
@NonNull
return null == this.address ? "" : this.address;
}

MyActivity.java
Button btnFoo;
TextView tvBar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnFoo = (Button) findViewById(R.id.btn_foo);
tvBar = (TextView) findViewById(R.id.tv_bar);
...
}

Intents.java
Intent intent = new Intent(this, OtherActivity.class);
intent.putExtra("id", 10L);
intent.setFlag(Intent.FLAG_ACTIVITY_SINGLE_TOP);
startActivity(intent);

MyActivity.java
btnDoIt.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO
}
});

MyActivity.kt
btnDoIt.setOnClickListener(object : View.OnClickListener() {
override fun onClick(v: View) {
// TODO
}
})

MyActivity.kt
btnDoIt.setOnClickListener({ v: View ->
// TODO
})

MyActivity.kt
btnDoIt.setOnClickListener({ v ->
// TODO
})

MyActivity.kt
btnDoIt.setOnClickListener({
it.context // View.context
})

MyActivity.kt
btnDoIt.setOnClickListener {
it.context // View.context
}

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

StandardLibrary.kt
people.filter { it.startsWith('S') }
.onEach { String::toUpperCase() }
.forEach { ::println }

StandardLibrary.kt
 
people.stream()
.filter { it.startsWith('S') }
.map(String::toUpperCase)
.forEach(::println)

User.java
// class User
var address: String? = null
////
val user : User = getCurrentUser()
user.address?.toUpperCase()

User.java
// class User
////
val user = getCurrentUser()
user.address?.toUpperCase()

User.java
// class User
get() = field ?: ""
////
val user = getCurrentUser()
user.address.toUpperCase()

MyActivity.kt
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
btn_foo // (Button) findViewById(R.id.btn_foo)
tv_bar // (TextView) findViewById(R.id.tv_bar)
...
}

Intents.kt
val intent = Intent(this, OtherActivity::class.java)
intent.putExtra("id", 10L)
intent.setFlag(Intent.FLAG_ACTIVITY_SINGLE_TOP)
startActivity(intent)

Intents.kt
startActivity(
intentFor<SomeOtherActivity>("id" to 10L).singleTop())

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

Collections.kt
val emptyStringList = listOf<String>()
val cities = listOf("Seoul", "Busan")
val mutableCities = mutableListOf("Seoul, Busan")
val emptyStringSet = setOf<String>()
val cities = setOf("Seoul", "Busan")
val mutableCities = mutableSetOf("Seoul, Busan")

Collections.kt
val pair : Pair<String, String> = Pair("Seoul", "SEO")

Collections.kt
val pair : Pair<String, String> = Pair("Seoul", "SEO")
// with stdlib
val pair : Pair<String, String> = "Seoul" to "SEO"

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

Person.java
public class Person {
String name;
String address;
Person(String name, String address) {
this.name = name;
}
public String getAddress() {
return address;
}
public void setAddress(String 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 != null ? !name.equals(person.name) : person.name != null) return false;
return address != null ? address.equals(person.address) : person.address == null;
}
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (address != null ? address.hashCode() : 0);
return result;
}
}

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

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

MyToast.kt
// 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!")

Extended
Seoul
ㅍ
Extended
Seoul

Kotlin: Let's Make Android Great Again

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Kotlin: Let's Make Android Great Again

Similar to Kotlin: Let's Make Android Great Again (20)

More from Taeho Kim

More from Taeho Kim (8)

Recently uploaded

Recently uploaded (20)

Kotlin: Let's Make Android Great Again