KOTLIN - Clase (ziua 4)

 Interfețe

- public by default

- nu există implements / extends

interface Time {
    fun setTime(hrs: Int, mins: Int = 0, secs: Int = 0)
    fun setTime(time: String) = setTime(0) // default implementation
}

interface NoTime {
    fun setTime(time: String) {}
}

class MyTime : Time, NoTime {
    override fun setTime(hrs: Int, mins: Int, secs: Int) {}

    override fun setTime(time: String) {
        super<Time>.setTime(time)
        super<NoTime>.setTime(time)
    }
}

Clase

- public, final by default (și metodele sunt final by default)

- dacă vrei să nu fie final - se specifică open

In Java era o practică bună să adaugi final claselor care nu trebuiesc extinse

- suport pt abstract

- clase sigilate (sealed)

- internal: clase vizibile doar în modulul respectiv 

- protected, private; dar nu există package private

open abstract class Person () {
    var firstName: String = ""
    var lastName: String = ""

    open fun getName(): String = "$firstName $lastName" // can be overriden

    abstract fun getWork() // can be implemented

    fun getVacations() {} // cannot be overriden
}

class Student : Person() {
    override fun getName(): String{return ""}
    override fun getWork() {
        TODO("Not yet implemented")
    }
}

Clase sigilate

- ierarhizare, asemănare cu enum

sealed class PersonEvent {
    // nested subclasses
    class Awake: PersonEvent()
    class Asleep: PersonEvent()
    class Eating(val food: String): PersonEvent()
}

fun handlePersonEvent(event: PersonEvent) =
    when(event) {
        is PersonEvent.Awake -> println("Awake")
        is PersonEvent.Asleep -> println("Asleep")
        is PersonEvent.Eating -> println("Eating ${event.food}")
    }

Constructori

open class Person (_fname: String, _lname: String) {
    var firstName: String = ""
    var lastName: String = ""

    init {
        this.firstName = _fname
        this.lastName = _lname
    }

    constructor(name: String) : this(name, "")

}

class Student : Person {
    var age: Int;
    init {
        age = 0;
    }

    constructor(name: String) : super(name)

    constructor(first: String, last: String) : super(first, last)

    constructor(first: String, last: String, age: Int) : super(first, last) {
        this.age = age;
    }

}

Data classes

- furnizează metodele toString, equals, hashCode + metoda copy pentru clonare

- sunt clase imutabile

- introdusă prin keywork data class

fun main(args: Array<String>) {
    var st1 = Steward(1, "Lina")
    var st2 = Steward(1, "Lina")
    var st3 = st2.copy(name = "Roberta") // toate câmpurile la fel mai puțin name

    println("Equal? ".plus(st1 == st2)) // true numai dacă există keyword data peste Steward
    println(st3) // apelează toString, rezultat citibil față de un Steward@5e2de80c, dacă nu era data
}

data class Steward(val id: Int, val name: String)