🏃‍♂️ Hızlı Notlar

🕐 Zaman Hesaplama

val time = measureTimeMillis {
val one = doSomethingUsefulOne()
val two = doSomethingUsefulTwo()
println("The answer is ${one + two}")
}
println("Completed in $time ms")

📋 Hepsi

// TODO
fun calcTaxes(): BigDecimal = TODO("Waiting for feedback from accounting")
// Koşullu kullanım (Conditional expressions)
if (a > b) a else b
// Instance check
when (x) {
is Foo -> // ...
is Bar -> // ...
else -> // ...
}
(obj !is String)
// Range
for (x in 1..10 step 2) {}
// Collections
val fruits = listOf("banana", "avocado", "apple", "kiwifruit")
fruits
.filter { it.startsWith("a") }
.sortedBy { it }
.map { it.toUpperCase() }
.forEach { println(it) }
("jane@example.com" !in emailsList)
// Filtreleme
list.filter { x -> x > 0 }
// Lazy
val p: String by lazy {
// compute the string
}
// Extension functions
fun String.spaceToCamelCase() { /* ... */ }
// Null
println(files?.size ?: "empty")
val mapped = value?.let { transformValue(it) } ?: defaultValue
val email = values["email"] ?: throw IllegalStateException("Email is missing!")
// Try-Catch
val email = values["email"] ?: throw IllegalStateException("Email is missing!")
fun transform(color: String): Int {
return when (color) {
"Red" -> 0
"Green" -> 1
"Blue" -> 2
else -> throw IllegalArgumentException("Invalid color param value")
}
}
fun test() {
val result = try {
count()
} catch (e: ArithmeticException) {
throw IllegalStateException(e)
}
// Working with result
}
fun transform(color: String): Int = when (color) {
"Red" -> 0
"Green" -> 1
"Blue" -> 2
else -> throw IllegalArgumentException("Invalid color param value")
}
// Java 7's try with resources
val stream = Files.newInputStream(Paths.get("/some/file.txt"))
stream.buffered().reader().use { reader ->
println(reader.readText())
}
// Convenient form for a generic function that requires the generic type information
// public final class Gson {
// ...
// public <T> T fromJson(JsonElement json, Class<T> classOfT) throws JsonSyntaxException {
// ...
inline fun <reified T: Any> Gson.fromJson(json: JsonElement): T = this.fromJson(json, T::class.java)
// Swap var
var a = 1
var b = 2
a = b.also { b = a }

Functions vs Properties

In some cases functions with no arguments might be interchangeable with read-only properties. Although the semantics are similar, there are some stylistic conventions on when to prefer one to another.

Prefer a property over a function when the underlying algorithm:

  • does not throw

  • is cheap to calculate (or caсhed on the first run)

  • returns the same result over invocations if the object state hasn't changed

Platform types

A public function/method returning an expression of a platform type must declare its Kotlin type explicitly:

fun apiCall(): String = MyJavaApi.getProperty("name")

Any property (package-level or class-level) initialised with an expression of a platform type must declare its Kotlin type explicitly:

class Person {
val name: String = MyJavaApi.getProperty("name")
}

A local value initialized with an expression of a platform type may or may not have a type declaration:

fun main() {
val name = MyJavaApi.getProperty("name")
println(name)
}

📝 Dokümantasyon Oluşturucu'