[Kotlin] 클래스 정리

Class 기본 사용

class User {

    var loggedIn: Boolean = false
    val cantChangeValue = "Hi"
    
    fun logOn() {
        loggedIn = true
    }
    
    fun logOff() {
        loggedIn = false
    }
}

fun main(args: Array<String>) {

    val user = User()
    println(user.loggedIn) //false
    user.logOn()
    println(user.loggedIn) //true
    user.logOff()
    println(user.loggedIn) //false
    user.cantChangeValue = "Hey" //won't compile. Can't modify a final variable.

}

Class 생성자 "init"

예 1.) =============================

class MultiInit(name: String) {

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

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

fun main(args: Array<String>) {
    var multiInit = MultiInit("Kotlin")
}

출력>>>>>>>
I/System.out: First initializer block that prints Kotlin
I/System.out: Second initializer block that prints 6


예 2.) ========= With "also"===========

class MultiInit(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}")
    }
}

fun main(args: Array<String>) {

    var multiInit = MultiInit("Kotlin")
}

출력>>>>>>>
I/System.out: First property: Kotlin
I/System.out: First initializer block that prints Kotlin
I/System.out: Second property: 6
I/System.out: Second initializer block that prints 6

Class 보조 생성자 "constructor"

class Student {
    var name: String
    val age : Int

    constructor(name: String, age: Int)
    {
        this.name = name
        this.age = age
    }

    fun printDetails()
    {
        println("Name is $name and Age is $age")
    }

}

fun main(args: Array<String>) {

    var student = Student("gugu", 17)
    student.printDetails()
}

출력 >>>>>>>>
//Name is gugu and Age is 17

init + constructor

class Student(var name: String, val age: Int) {

    var skill: String

    init {
        skill = "play"
    }

    constructor(name: String, age: Int, skill: String) : this(name, age) {
        this.skill = skill
    }

    fun printDetails() {
        if (skill.equals("play"))
            println("Name is $name and Age is $age")
        else
            println("Name is $name and Age is $age Skill is $skill")
    }
}

I/System.out: Name is no-b-rain and Age is 1
I/System.out: Name is dudu and Age is 20 Skill is dodory

 

생성자의 인수 , 인수의 기본값 설정

예 1.) 
class User(name: String, val isAdmin: Boolean) {

    var username = name     //username = name
    val _isAdmin = isAdmin  //_isAdmin = isAdmin

    init {
        username= username + "https://no-b-rain.tistory.com/"
        println("Author Name is $name. Is Admin? $_isAdmin")
    }
}

fun main(args: Array<String>) {

    var user = User("no-b-rain",false)
    // Error Code : user.isAdmin = true  //won't compile since isAdmin is val
    // Error Code : user._isAdmin = true //won't compile. Same reason.
    user = User("no-Brain",true)
}



예 2.) 
class User(name: String, var website: String = "no-b-rain") {

    init {
        println("Author $name writes at $website")
    }

    init {
        website = website + ".com"
        println("Author $name writes at $website")
    }
}

fun main(args: Array<String>) {

    var user = User("no-b-rain","dudu")
    user = User("no-Brain","dudu")
}

I/System.out: Author no-b-rain writes at dudu
I/System.out: Author no-b-rain writes at dudu.com
I/System.out: Author no-Brain writes at dudu
I/System.out: Author no-Brain writes at dudu.com

커스텀  setter , getter

class Name{
    var post: String = "default"
    set(value) {if(!post.isNotEmpty()) {
        throw IllegalArgumentException(" Enter a valid name")
    }
                field = value
    }
    get() {
        return field.capitalize()
    }

}

fun main(args: Array<String>) {

    var name = Name()
    name.post = "kotlin classes"
    println(name.post)
    name.post = "kotlin data Classes our next Tutorial"
    println(name.post)

}

abstract

abstract class Person(name: String) {

    init {
        println("Abstract Class. init block. Person name is $name")
    }

    abstract fun displayAge()
}

class Teacher(name: String): Person(name) {

    var age : Int

    init {
        age = 24
    }

    override fun displayAge() {
        println("Non-abstract class displayAge function overridden. Age is $age")
    }
}

fun main(args: Array<String>) {

    val person = Teacher("Anupam")
    person.displayAge()

}

//Following is printed in the console.
//Abstract Class. init block. Person name is Anupam
//Non-abstract class. Age is 24