As i have one User class having 2 parameters : first_name, last_name. So my kotlin class with be :
data class User(val first_name:String, val last_name:String) Now i want a constructor which will accept only first_name, or you can say just one parameter. How can i define it with Kotlin?
I know we can pass default value and in that way we can ignore second parameter, but how can we write multiple constructor?
You can define extra constructors in the class body
data class User(val firstName: String, val lastName: String) { constructor(firstName: String) : this(firstName, "") } These 'secondary constructors' have to call through to the primary constructor or a different secondary constructor. See the Official documentation on constructors.
So, in effect this is the same as just a primary constructor with default argument, which would be the idiomatic way to go.
data class User(val firstName: String, val lastName: String = "") I hope this will help you
class Person(val name: String, val age: Int = 0) { override fun toString(): String { return name + " is " + age + " years Old" } } fun main(args: Array<String>) { var person = Person(name = "vignesh") var personNew = Person("vignesh", 23) println(person.toString()) println(personNew.toString()) } Output
vignesh is 0 years Old
vignesh is 23 years Old
If you are using data class, then you won't require another constructor. Just pass default value to your last_name parameter. If you are using a normal class then you can have secondary constructor Lets say you have class A
class A(val param:String,val param2:String){ constructor(val param:String):this(param,"") } If you wish manipulate these values you can use init{} block where you can play around your constructor values.
I hope this will help.
This sample of code works fine for me, you can customize them to your need.
data class Booking( var user: String, var bike: String ){ constructor( user: String, bike: String, taken_at: String, returned_at: String ) : this (user, bike) } 
val x = Booking("foo", "bmx", "10am", "1030pm"), how can we print out the values for taken_at and returned_at? seems like we can't do: println(x.taken_at) it doesn't work.
A class in Kotlin can have a primary constructor and one or more secondary constructors. The primary constructor is part of the class header: it goes after the class name (and optional type parameters).
class Person constructor(firstName: String) { } If the primary constructor does not have any annotations or visibility modifiers, the constructor keyword can be omitted:
class Person(firstName: String) { } Note that parameters of the primary constructor can be used in the initializer blocks. They can also be used in property initializers declared in the class body:
class Customer(name: String) { val customerKey = name.toUpperCase() } You can also follow this link as per your need : Kotlin
