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Kotlin profile

Kotlin is a cross-platform static programming language developed by JetBrains. It is currently managed by the Kotlin Foundation, a joint venture between JetBrains and Google. Kotlin can seamlessly interact with Java code and is the preferred language for Android development. Brief development history:

• 2011.07 JetBrains launched a new JVA-BASED language :Kotlin. Kotlin takes its name from the Island of Kotlin, near St. Petersburg, Russia.
• 2016.02 Kotlin released the first stable release: V1.0
• Google announced Kotlin as a Level 1 Support language for Android development at the I/O conference in May 2017.
• 2017.11 Kotlin supports compiling to JavaScript.
• Kotlin introduced coroutines to simplify asynchronous programming.
• In May 2019, Google announced Kotlin as the preferred language for Android development at I/O.

Variable Definition (constant)

1. Variable definition var Variable name [: type] [= initial value] Example:

var a: Int = 1
var b = 1   // The system automatically concludes that the variable type is Int
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2. Definition of an immutable variable (cannot be modified after being defined) val Name of the variable [: type] [= initial value] Example:

val a: Int = 1
val b = 1   // The system automatically concludes that the variable type is Int
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Underlying data types

1. Boolean Value Boolean values can be true or false. Example:

var flag: Boolean = true
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2. Digital type

Sample:

var i: Byte = 1
var j: Short = 1
var k: Int = 1
var l: Long = 1
var m: Double = 1.0
var n: Float = 1f
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3. character

var char:Char='a'
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4. String type

var name: String = "jack"
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Under controlled conditions

• If – else

var name = Anonymous
if (name == "Sun Wukong") {
    print("The risk")}else {
    print("Human")}Copy the code

• S the way

var name = Anonymous
when (name) {
    "Sun Wukong" -> print("The risk")
    else -> print("Human")}Copy the code

Cycle control

• The for loop

var list = listOf(1.2.3)
for (item: Int in list) {
    println(item)
}
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for (item: Int in 1.10.) {
    println(item)
}

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• The while loop

var value = 5
while (value > 0) {
    println( value--)
}
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• The do while loop

var value = 5
do {
    println(value--)
} while (value > 0)
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function

class

The Kotlin class can contain: constructors, initializer code, functions, attributes, and inner classes. Sample:

• The empty class

class User
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• Classes with attributes

class User() {
    var name: String = "Empty."
}
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• Contains attributes and default constructors

class User(var name:String)
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• Data classes automatically add toString(), hashCode(), equals(), and copy() methods

data class User(var name:String)
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• Class in the constructor

class User(var name: String) {
    init {
        println("Initialize in constructor")}}Copy the code

• multiconstructor

class User(var name: String, var age: Int.var gender: String) {
    init {
        print("Default constructor")}constructor(name: String, age: Int) : this(name, age, "M") {
        print("Another constructor")}constructor(name: String) : this(name, 18) {
        print("Let's have another constructor.")}}Copy the code

interface

The interface keyword declaration supports defining methods (which can have default implementations) and properties.

• Defines the interface

interface MyInterface {
    fun test1(a)    / / unrealized
    fun test2(a) {  / / has been realized
        // Optional method body
        println("Ha ha")}// Can be overridden
    val name: String
}
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• Class implementation interface

class Student(override val name: String) : Exam {
    override fun exam1(a) {
        println("${name}Retake")}}Copy the code

annotation

• Single-line comments, using //

// Single-line comment
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• Multi-line comments, using /* */

/* Multi-line comments */
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• For document comments, use /** */

/** **
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Android development tutorial series summary

Android development history and prospects

Android development history Outlook of Android development

A preliminary study on the android

Install developer tools to create your first Android project

Development language learning

Kotlin language basics

UI control learning series

UI control _TextView UI control _EditText UI control _Button UI control _ImageView UI control _RadioButton UI control _CheckBox UI control _ProgressBar

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