WHAT IS KOTLIN ? IS IT A "SWIFT" FOR ANDROID ? ~ Discovery Android

1.Kotlin la gì ?

Kotlin là 1 ngôn ngữ lập trình hàm giồng như Swift trên nền tảng JVM , với khả năng tương tác cao với Java . Kotlin độc nhất ở thư viện tiêu chuẩn và runtime của nó là rất nhỏ trong byte, nhưng rất là mạnh mẽ . Phần lớn được loại trừ khi compile (trái ngược với scala) nên nó có thể sử dụng trong môi trường mà bộ nhớ bị hạn chế như Android (nhưng mà là smartphone chứ không phải hệ thống nhúng)

2. Cài đặt Kotlin trong Android Studio

Trong android studio , chọn Configure -> Plugin , hoặc chọn menu Preferences

Trong màn hình kế tiếp , nhấn vào Install JetBrains plugin .. ở phía dưới

Chọn Kotlin Extensions For Android từ danh sách và nhấp vào Install Plugin ở phía bên phải

Restart Android Studio và thưởng thức Kotlin

3.Kotlin(Android) có vài nét tương đồng với Switft(iOS) . Dưới đây là sự so sánh giữa Kotlin và Swift

Hello World

Swift

print("Hello, world!")

Kotlin

println("Hello, world!")

Variables And Constants

Swift

var myVariable = 42
myVariable = 50
let myConstant = 42

Kotlin

var myVariable = 42
myVariable = 50
val myConstant = 42

Explicit Types

Swift

let explicitDouble: Double = 70

Kotlin

val explicitDouble: Double = 70.0

Type Coercion

Swift

let label = "The width is "
let width = 94
let widthLabel = label + String(width)

Kotlin

val label = "The width is "
val width = 94
val widthLabel = label + width

String Interpolation

Swift

let apples = 3
let oranges = 5
let fruitSummary = "I have \(apples + oranges) " +
                   "pieces of fruit."

Kotlin

val apples = 3
val oranges = 5
val fruitSummary = "I have ${apples + oranges} " +
                   "pieces of fruit."

Range Operator

Swift

let names = ["Anna", "Alex", "Brian", "Jack"]
let count = names.count
for i in 0..<count {
    print("Person \(i + 1) is called \(names[i])")
}
// Person 1 is called Anna
// Person 2 is called Alex
// Person 3 is called Brian
// Person 4 is called Jack

Kotlin

val names = arrayOf("Anna", "Alex", "Brian", "Jack")
val count = names.count()
for (i in 0..count - 1) {
    println("Person ${i + 1} is called ${names[i]}")
}
// Person 1 is called Anna
// Person 2 is called Alex
// Person 3 is called Brian
// Person 4 is called Jack

Inclusive Range Operator

Swift

for index in 1...5 {
    print("\(index) times 5 is \(index * 5)")
}
// 1 times 5 is 5
// 2 times 5 is 10
// 3 times 5 is 15
// 4 times 5 is 20
// 5 times 5 is 25

Kotlin

for (index in 1..5) {
    println("$index times 5 is ${index * 5}")
}
// 1 times 5 is 5
// 2 times 5 is 10
// 3 times 5 is 15
// 4 times 5 is 20
// 5 times 5 is 25

COLLECTIONS

Arrays

Swift

var shoppingList = ["catfish", "water",
    "tulips", "blue paint"]
shoppingList[1] = "bottle of water"

Kotlin

val shoppingList = arrayOf("catfish", "water",
    "tulips", "blue paint")
shoppingList[1] = "bottle of water"

Maps

Swift

var occupations = [
    "Malcolm": "Captain",
    "Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"

Kotlin

val occupations = mutableMapOf(
    "Malcolm" to "Captain",
    "Kaylee" to "Mechanic"
)
occupations["Jayne"] = "Public Relations"

Empty Collections

Swift

let emptyArray = [String]()
let emptyDictionary = [String: Float]()

Kotlin

val emptyArray = arrayOf<String>()
val emptyMap = mapOf<String, Float>()

FUNCTIONS

Functions

Swift

func greet(_ name: String,_ day: String) -> String {
    return "Hello \(name), today is \(day)."
}
greet("Bob", "Tuesday")

Kotlin

fun greet(name: String, day: String): String {
    return "Hello $name, today is $day."
}
greet("Bob", "Tuesday")

Tuple Return

Swift

func getGasPrices() -> (Double, Double, Double) {
    return (3.59, 3.69, 3.79)
}

Kotlin

data class GasPrices(val a: Double, val b: Double,
     val c: Double)
fun getGasPrices() = GasPrices(3.59, 3.69, 3.79)

Variable Number Of Arguments

Swift

func sumOf(_ numbers: Int...) -> Int {
    var sum = 0
    for number in numbers {
        sum += number
    }
    return sum
}
sumOf(42, 597, 12)

Kotlin

fun sumOf(vararg numbers: Int): Int {
    var sum = 0
    for (number in numbers) {
        sum += number
    }
    return sum
}
sumOf(42, 597, 12)

// sumOf() can also be written in a shorter way:
fun sumOf(vararg numbers: Int) = numbers.sum()

Function Type

Swift

func makeIncrementer() -> (Int -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
let increment = makeIncrementer()
increment(7)

Kotlin

fun makeIncrementer(): (Int) -> Int {
    val addOne = fun(number: Int): Int {
        return 1 + number
    }
    return addOne
}
val increment = makeIncrementer()
increment(7)

// makeIncrementer can also be written in a shorter way:
fun makeIncrementer() = fun(number: Int) = 1 + number

Map

Swift

let numbers = [20, 19, 7, 12]
numbers.map { 3 * $0 }

Kotlin

val numbers = listOf(20, 19, 7, 12)
numbers.map { 3 * it }

Sort

Swift

var mutableArray = [1, 5, 3, 12, 2]
mutableArray.sort()

Kotlin

listOf(1, 5, 3, 12, 2).sorted()

Named Arguments

Swift

func area(width: Int, height: Int) -> Int {
    return width * height
}
area(width: 2, height: 3)

Kotlin

fun area(width: Int, height: Int) = width * height
area(width = 2, height = 3)

// This is also possible with named arguments
area(2, height = 2)
area(height = 3, width = 2)

CLASSES

Declaration

Swift

class Shape {
    var numberOfSides = 0
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

Kotlin

class Shape {
    var numberOfSides = 0
    fun simpleDescription() =
        "A shape with $numberOfSides sides."
}

Usage

Swift

var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()

Kotlin

var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()

Subclass

Swift

class NamedShape {
    var numberOfSides: Int = 0
    let name: String

    init(name: String) {
        self.name = name
    }

    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

class Square: NamedShape {
    var sideLength: Double

    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        super.init(name: name)
        self.numberOfSides = 4
    }

    func area() -> Double {
        return sideLength * sideLength
    }

    override func simpleDescription() -> String {
        return "A square with sides of length " +
        sideLength + "."
    }
}

let test = Square(sideLength: 5.2, name: "square")
test.area()
test.simpleDescription()

Kotlin

open class NamedShape(val name: String) {
    var numberOfSides = 0

    open fun simpleDescription() =
        "A shape with $numberOfSides sides."
}

class Square(var sideLength: BigDecimal, name: String) :
        NamedShape(name) {
    init {
        numberOfSides = 4
    }

    fun area() = sideLength.pow(2)

    override fun simpleDescription() =
        "A square with sides of length $sideLength."
}

val test = Square(BigDecimal("5.2"), "square")
test.area()
test.simpleDescription()

Checking Type

Swift

var movieCount = 0
var songCount = 0

for item in library {
    if item is Movie {
        movieCount += 1
    } else if item is Song {
        songCount += 1
    }
}

Kotlin

var movieCount = 0
var songCount = 0

for (item in library) {
    if (item is Movie) {
        ++movieCount
    } else if (item is Song) {
        ++songCount
    }
}

Pattern Matching

Swift

let nb = 42
switch nb {
    case 0...7, 8, 9: print("single digit")
    case 10: print("double digits")
    case 11...99: print("double digits")
    case 100...999: print("triple digits")
    default: print("four or more digits")
}

Kotlin

val nb = 42
when (nb) {
    in 0..7, 8, 9 -> println("single digit")
    10 -> println("double digits")
    in 11..99 -> println("double digits")
    in 100..999 -> println("triple digits")
    else -> println("four or more digits")
}

Downcasting

Swift

for current in someObjects {
    if let movie = current as? Movie {
        print("Movie: '\(movie.name)', " +
            "dir. \(movie.director)")
    }
}

Kotlin

for (current in someObjects) {
    if (current is Movie) {
        println("Movie: '${current.name}', " +
     "dir. ${current.director}")
    }
}

Protocol

Swift

protocol Nameable {
    func name() -> String
}

func f<T: Nameable>(x: T) {
    print("Name is " + x.name())
}

Kotlin

interface Nameable {
    fun name(): String
}

fun f<T: Nameable>(x: T) {
    println("Name is " + x.name())
}

Extensions

Swift

extension Double {
    var km: Double { return self * 1_000.0 }
    var m: Double { return self }
    var cm: Double { return self / 100.0 }
    var mm: Double { return self / 1_000.0 }
    var ft: Double { return self / 3.28084 }
}
let oneInch = 25.4.mm
print("One inch is \(oneInch) meters")
// prints "One inch is 0.0254 meters"
let threeFeet = 3.ft
print("Three feet is \(threeFeet) meters")
// prints "Three feet is 0.914399970739201 meters"

Kotlin

val Double.km: Double get() = this * 1000
val Double.m: Double get() = this
val Double.cm: Double get() = this / 100
val Double.mm: Double get() = this / 1000
val Double.ft: Double get() = this / 3.28084

val oneInch = 25.4.mm
println("One inch is $oneInch meters")
// prints "One inch is 0.0254 meters"
val threeFeet = 3.0.ft
println("Three feet is $threeFeet meters")
// prints "Three feet is 0.914399970739201 meters"

Sunday, May 28, 2017