Kickstart Kotlin

Kickstart Kotlin
Zahidur Rahman Faisal

Why use Kotlin?
● Simple syntax, easy to read / write
● Powerful features from many other modern languages
● Goodbye NullPointerExceptions
● Completely interoperable with Java
● Great IDE and tooling support
● Code less, do more
● Similarity with Swift, JavaScript or Python

Kickstart Kotlin
Preferences (OSX)
or Settings (Windows/Linux)
> Plugins
> Browse Repositories
> Search “Kotlin”
> Restart Android Studio

Convert your JAVA class
> Select your .java file (Ex: MainActivity.java)
> Code
> Convert Java file to Kotlin file

Goodbye NPE
var nonNullString: String = "Droidcon"
nonNullString = null // Compilation error
val size = nonNullString.length
var nullableString: String? = "Droidcon"
nullableString = null // Compiles fine
val size = nullableString.length // Error:
variable 'nullableString' can be null
val size = nullableString?.length // Null safe

Elvis (Presley?) to the rescue
// Returns length of the String -1 if the String is null
val size = nullableString?.length ?: -1

class Droidcon {
var country: Country?
var host: String?
}
class Country {
var venue: Venue?
var ticketPrice: Int
}
class Venue {
var location: String?
var vanueName: String?
}
JAVA
if (droidCon != null) {
if (droidCon.country != null) {
if (droidCon.country.venue != null) {
... ... ...
println(droidCon.country.venue.location);
}
}
}
No insane sanity checks
Kotlin
print(droidCon?.country?.venue?.location)

POJO vs Data Class
POJO
public class DroidconEvent {
public String topic;
public String speaker;
public long time;
public DroidconEvent(String topic, String speaker, long time) {
this.topic = topic;
this.speaker = speaker;
this.time = time;
}
}
Data Class
data class DroidconEvent(val topic: String,
var speaker: String, val time: Long)

Lazy Lambdas
JAVA
mButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(this, "Hello Droidcon!",
Toast.LENGTH_SHORT).show();
}
};
Kotlin
mButton.setOnClickListener {
Toast.makeText(this, "Hello Droidcon!", Toast.LENGTH_SHORT).show()
}

Set with “with()”
JAVA
mTextView.setText("Hello Droidcon");
mTextView.setTextSize(30f);
mTextView.setTextColor(Color.WHITE);
mTextView.setBackgroundColor(Color.BLACK);
Kotlin
with (mTextView) {
text = "Hello Droidcon!"
textSize = 30f
setTextColor(Color.WHITE)
setBackgroundColor(Color.BLACK)
}

“When” is the new “Case”
when (x) {
0 -> print("x is 0") // x == 0
in 1..10 -> print("x is in the range") // x inside range 1 - 10
in validNumbers -> print("x is valid") // x is in a collection “validNumbers”
!in 10..20 -> print("x is outside the range") // x is outside range 10 - 20
else -> print("none of the above") // default case
}

Exclusive Extensions
Extension function: (for navigating to a new Activity)
fun Activity.navigateTo(activity: Activity, bundle: Bundle?) {
val intent = Intent(this, activity.javaClass)
bundle ?: intent.putExtra("bundle", bundle)
startActivity(intent)
}
Usage: (from any Activity)
navigateTo(AnotherActivity(), null)

Funny Functions: Default arguments
fun incrementSteps(currentSteps: Int, increment: Int = 1): Int {
return currentSteps + increment
}
Usage:
incrementSteps(5) // Returns 6
incrementSteps(5, 3) // Returns 8

Funny Functions: Named Arguments
fun incrementSteps(currentSteps: Int, increment: Int = 1): Int {
return currentSteps + increment
}
Usage:
incrementSteps(currentSteps = 5, increment = 2) // Returns 7

Funny Functions: Single-Expression Functions
fun doubleSteps(currentSteps: Int) = currentSteps * 2
Usage:
doubleSteps(5) // Returns 10

Funny Functions: Varargs (Variable Arguments)
fun getSum(vararg numbers: Int): Int {
var sum = 0
for (number in numbers) {
sum += number
}
return sum
}
Usage:
getSum(1, 2, 3) // Returns 6
getSum(1, 2, 3, 4, 5) // Returns 15

More Kotlin Awesomeness
https://kotlin.link
http://try.kotlinlang.org
https://github.com/Kotlin/kotlin-koans
https://www.facebook.com/groups/1289612087746759/

Kickstart Kotlin

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