Can Kotlin data class have more than one constructor?

Question

I know that data class are like simple models in kotlin with getters and setter by default and are as simple this:

data class User(val name: String, val age:         


        

Answer 1

Updated answer for data classes:

Yes you can, but you will need to delegate everything to the primary constructor

data class User(val name: String, val age: Int)
{
    constructor(name: String): this(name, -1) {
    }

    constructor(age: Int): this("Anon", age) {
    }
}

// Anon name: Anon
println("Anon name: " + User(30).name)

// No age: -1
println("No age: " + User("Name").age)

// Name: Name age: 20
val u = User("Name", 20)
println("Name: " + u.name + " age: " + u.age)

You can also set default values in your primary constructor as Alexey did.

Answer 2

you can set the data class like this

data class User(val name: String? = null, val id: String? = null, val email: String? = null)

and you can instance the object with multiple constructors like this

val userId = User(id = "123456")
        val userMail = User(email= "email@email.com")
        val userName = User("Name")

Answer 3

Data class will ensure consistency and meaningful behavior also we need to have val for immutability.

data class SampleData(val name: String, val age: Int, val email: String ?= null) {
constructor(name: String, age: Int) : this(name, age, null) {

}

}

secondary constructor must delegate to the primary constructor in its definition, so to maintain the immutability, having "null" will work.

Answer 4

I wanted to have a class similar to below (with a constructor that parses an input)

data class Data(val a: String, val b: String) {
    constructor(spaceSeparated: String) { // error because we don't call this()
        val split = spaceSeparated.split(" ")
        this(split.first(), split.last()) // error again because it's not valid there
    }
}

The solution is to do this:

data class Data(val a: String, val b: String) {
    companion object {
        operator fun invoke(spaceSeparated: String): Data {
            val split = spaceSeparated.split(" ")
            return Data(split.first(), split.last())
        }
    }
}

And it can be called just as if it were a constructor

Answer 5

Default values in the primary constructor eliminates many needs for secondary constructors, but if the needed instance depends on logic based on data that must be analyzed the better answer may be to use a companion object.

data class KeyTag(val a: String, val b: Int, val c: Double) {
    companion object Factory {
        val empty = KeyTag("", 0, 0.0)

        fun create(bigString: String): KeyTag {
            // Logic to extract appropriate values for arguments a, b, c
            return KeyTag(a, b, c)
        }

        fun bake(i: Int): KeyTag = KeyTag("$i", i, i.toDouble())
    }
}

Usage is then:

val ks = KeyTag.create("abc:1:10.0")
val ke = KeyTag.empty
val kb = KeyTag.bake(2)

Answer 6

Instructs the Kotlin compiler to generate overloads for this function that substitute default parameter values. If a method has N parameters and M of which have default values, M overloads are generated: the first one takes N-1 parameters (all but the last one that takes a default value), the second takes N-2 parameters, and so on.

 data class User @JvmOverloads  constructor(
var email: String="",
var password: String="")