Bye Java, hello Kotlin alias What do we love about Kotlin @Synetech

Constructors.kt

class InitOrderDemo(name: String) {
    val firstProperty = "First property: $name".also(::println)

    init {
        println("First initializer block that prints ${name}")
    }

    val secondProperty = "Second property: ${name.length}".also(::println)

    init {
        println("Second initializer block that prints ${name.length}")
    }
}

InitOrderDemo("hello")

DataClasses.kt

// Example of data class (saved more than 10 lines in comparison to Java)
data class User(val name: String, val surname: String, val age: Int)

// Example of custom getters and setters on a property
class MrUser {
    var name: String = ""
        get() {
            return "Mr. $field" // Get name with "Mr." prefix
        }
        set(newValue) {
            println("old: '$field', new: '$newValue'") // Print change
            field = newValue // Store new value
        }
}

DefaultValues.kt

fun logException(e: Throwable, level = Log.ERROR) {
    // implementation
}

// Then you can call the method without providing the second parameter
logException(IllegalStateException("Test exception"))
logException(IllegalStateException("Test exception"), Log.WARN)

DefaultValues2.kt

interface Greeter {
		fun greet() { println("Hi!") }
}

Elvis.kt

val a: Int? = 10
val b: Int = 10
val sum = a ?: 0 + b

Elvis2.kt

val sum = a ?: (0 + b)

Extensions.kt

fun View.makeInvisible() {
    this.visibility = View.INVISIBLE
}

val button: Button = //...
button.makeInvisible()

FunctionsAndLambdas.kt

data class User(val name)

interface UserDataSource {
    fun getAllUsers(
            onSuccess: (users: List<User>) -> Unit,
            onError: (err: Throwable) -> Unit
    )
}

// class UpdateDataSourceImpl: UserDataSource { .... }

UpdateDataSourceImpl().getAllUsers(
    onSuccess = { users -> print(users) }, // here you consume success state
    onError = { err -> print(err.message) } // here you consume error state
)

PropertyDelegates.kt

val answer: Int by lazy {
    computeAnswer()
}

fun computeAnswer() = 42

RangesInLoops.kt

var max = 10
for (i in 1..max) {
  // ...
}

RangesInLoops2.kt

int max = 10;
for (int i = 1 ; i <= max ; i++) {
	// ...
}

RangesInLoops3.kt

var max = 10
val range = IntRange(1, max)
for (i in range) {
	// ...
}

ScopeFunctions.kt

private const val DURATION_IN_MS = 3000L

val fadeInAnimation = AlphaAnimation(0f, 1f).apply {
    duration = DURATION_IN_MS
    interpolator = AccelerateDecelerateInterpolator()
    fillAfter = true
}

SealedClasses.kt

sealed class UIState
object LoadingState : UIState() // Data is being loaded
class DataState(val data: Data) : UIState() // Data loaded successfully
class ErrorState(val error: Throwable) : UIState() // In case of failure

SealedClasses2.kt

fun handleStateChange(newState: UIState) {
    when (newState) {
        is LoadingState -> println("Loading ...")
        is DataState -> println("Got data: ${newState.data}")
        is ErrorState -> println("Error: ${newState.error.message}")
    }
}

SingleExpression.kt

fun answerToEverything() = 42

SingleExpression2.kt

fun answerToEverything(): Int {
    return 42
}

SingleExpression3.kt

fun parseColor(color: String) = when (color.toLowerCase()) {
    "red" -> "#f00"
    "green" -> "#0f0"
    "blue" -> "#00f"
    else -> "#fff"
}