Yeah, that's a cool feature of Kotlin. As JPA requires, @Entity classes should have a default (non-arg) constructor to instantiate the objects when retrieving them from the database. So the line person.lastName = "Jobs" in Kotlin is … This way Kotlin knows that the value should be assigned to the second parameter last and not to the first parameter as it would have been if we didn't provide the parameter name. I could not find anything in the documentation, but I was hoping something like this would work: val data = Data(newName()?, newNumber()?) You can use one another constructor along with the primary constructor in Kotlin. In Kotlin, we can declare the breed property inside the Dog primary constructor and can also assign a default value. A constructor is a special kind of function and it is called as soon as the Class object is created. //all the 3 values are passed val person1 = Person("Pubg", 25, 100000) //update name and take the default value of age and salary val person2 = Person("John") //take all default value val person3 = Person() Secondary Constructor. What the challenge of using Kotlin and JSON boils down to is: We want to use Kotlin data classes for concise code, non-nullable types for null-safety and default arguments for the data class constructor to work when a field is missing in a given JSON. Using default parameters in a constructor is no different. This way, Kotlin can work well with such libraries as Jackson or JPA, which use the no-args constructor to create class instances: class Person(val name: String = "") ... Kotlin does not infer return types for functions with block bodies because such functions may have complex control flow in the body, and the return type will be non-obvious to the reader (and sometimes even for the compiler). We are assigning values to color and breed properties. A constructor is the most sophisticated way to initialize the properties of a class. A default value is defined using the = after the type. For this purpose, it’ll instantiate an object with default values. Kotlin constructors are bit different than other programming languages. Here, we have one class called User with two default parameters for the constructor : name and age.By default, name is an empty string and age is equal to 0. sayHello(last = "Doe") //>Hello Mr Doe Using default parameters in constructors. Default Values in the Constructor. But that does not compile. We can also provide default values for the properties of the class right inside the constructor - ... Kotlin internally calls the default (implicit) getters/setters of the properties. But is there a way to just use the default value specified in the constructor of the Data class when the values are null? There are two types of constructors in Kotlin. Java by design does not support optional parameters! Kotlin functions and constructors can define default arguments, allowing calls to them to skip any argument that has a default value. class Dog(var breed:String="labrador") : Animal() { } Now if we don’t pass any value for breed it will get “labrador” by default. Default values in Kotlin constructor. This is the normal scenario. Fortunately, Kotlin unlike Java, provide built-in support for this concept! Note that the compiler only uses the properties defined inside the primary constructor for the automatically generated functions. Sometimes, we want our code to be more flexible and reusable to handle default values for optional parameters in our constructors! 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