Data classes in Kotlin

Question

What is the difference between:

Definition 1

data class Person (var name:String, var age:Int)

Definition 2

class Person (va         


        

Answer 1

Definition 1 (data class Person(var name: String, var age: Int) is the equivalent of

/* every class by default in kotlin is final but a data class CAN'T be open */
final class Person(var name: String, var age: Int) {
    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other?.javaClass != javaClass) return false

        other as Person

        if (name != other.name) return false
        if (age != other.age) return false

        return true
    }

    override fun hashCode(): Int {
        var result = name.hashCode()
        result = 31 * result + age
        return result
    }
}

val person = Person("Name", 123)

Definition 2 (class Person(var name: String, var age: Int [no data modifier]) is the equivalent of

class Person(var name: String, var age: Int) {
}

val person = Person("Name", 123)

Definition 3 is the equivalent of

class Person() {
    var name: String = ""
    var age: Int = 1
}

val person = Person() // name = "", age = 1 (by default)
person.name = "Name"
person.age = 123