In past month i did some work on Kotlin and some article you can see on this trending topic. So today i am here with the list of daily used Kotlin code snippet which every developer need to know.
It is a collection of random and frequently used idioms in Kotlin. If you have a favorite idiom, contribute it by sending a comment below.
List of Daily used Kotlin Code Snippet
1Creating DTOs (POJOs/POCOs)
data class Customer(val name: String, val email: String)
provides a Customer
class with the following functionality:
- getters (and setters in case of var{: .keyword }s) for all properties
equals()
hashCode()
toString()
copy()
component1()
,component2()
, …, for all properties (see Data classes)
Do you know : What is Kotlin Native?
2Default values for function parameters
fun foo(a: Int = 0, b: String = "") { ... }
3Filtering a list
val positives = list.filter { x -> x > 0 }
Or alternatively, even shorter:
val positives = list.filter { it > 0 }
Do you use this : Koin – Kotlin Dependency Injection
4String Interpolation
println("Name $name")
5Instance Checks
when (x) { is Foo -> ... is Bar -> ... else -> ... }
6Traversing a map/list of pairs
for ((k, v) in map) { println("$k -> $v") }
k
, v
can be called anything.
7Using ranges
for (i in 1..100) { ... } // closed range: includes 100 for (i in 1 until 100) { ... } // half-open range: does not include 100 for (x in 2..10 step 2) { ... } for (x in 10 downTo 1) { ... } if (x in 1..10) { ... }
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8Read-only list
val list = listOf("a", "b", "c")
9Read-only map
val map = mapOf("a" to 1, "b" to 2, "c" to 3)
10Accessing a map
println(map["key"]) map["key"] = value
11Lazy property
val p: String by lazy { // compute the string }
Did you know : Disadvantage of Kotlin – You must know before use
12Extension Functions
fun String.spaceToCamelCase() { ... } "Convert this to camelcase".spaceToCamelCase()
13Creating a singleton
object Resource { val name = "Name" }
14If not null shorthand
val files = File("Test").listFiles() println(files?.size)
15If not null and else shorthand
val files = File("Test").listFiles() println(files?.size ?: "empty")
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16Executing a statement if null
val data = ... val email = data["email"] ?: throw IllegalStateException("Email is missing!")
17Execute if not null
val data = ... data?.let { ... // execute this block if not null }
18Map nullable value if not null
val data = ... val mapped = data?.let { transformData(it) } ?: defaultValueIfDataIsNull
19Return on when statement
fun transform(color: String): Int { return when (color) { "Red" -> 0 "Green" -> 1 "Blue" -> 2 else -> throw IllegalArgumentException("Invalid color param value") } }
20‘try/catch’ expression
fun test() { val result = try { count() } catch (e: ArithmeticException) { throw IllegalStateException(e) } // Working with result }
21‘if’ expression
fun foo(param: Int) { val result = if (param == 1) { "one" } else if (param == 2) { "two" } else { "three" } }
22Builder-style usage of methods that return Unit
fun arrayOfMinusOnes(size: Int): IntArray { return IntArray(size).apply { fill(-1) } }
23Single-expression functions
fun theAnswer() = 42
This is equivalent to
fun theAnswer(): Int { return 42 }
This can be effectively combined with other Kotlin code snippet, leading to shorter code. E.g. with the when{: .keyword }-expression:
fun transform(color: String): Int = when (color) { "Red" -> 0 "Green" -> 1 "Blue" -> 2 else -> throw IllegalArgumentException("Invalid color param value") }
Scratch tutorial : Create Reddit like Android Kotlin app Step by Step
24Calling multiple methods on an object instance (‘with’)
class Turtle { fun penDown() fun penUp() fun turn(degrees: Double) fun forward(pixels: Double) } val myTurtle = Turtle() with(myTurtle) { //draw a 100 pix square penDown() for(i in 1..4) { forward(100.0) turn(90.0) } penUp() }
25Java 7’s try with resources
val stream = Files.newInputStream(Paths.get("/some/file.txt")) stream.buffered().reader().use { reader -> println(reader.readText()) }
26Convenient 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)
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