Sometimes, we want our code to be more flexible and reusable to handle default values for optional parameters in our constructors! For this purpose, it’ll instantiate an object with default values. 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. A constructor is the most sophisticated way to initialize the properties of a class. Kotlin functions and constructors can define default arguments, allowing calls to them to skip any argument that has a default value. Fortunately, Kotlin unlike Java, provide built-in support for this concept! ... 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). So the line person.lastName = "Jobs" in Kotlin is … Yeah, that's a cool feature of Kotlin. I could not find anything in the documentation, but I was hoping something like this would work: val data = Data(newName()?, newNumber()?) But is there a way to just use the default value specified in the constructor of the Data class when the values are null? 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. Using default parameters in a constructor is no different. This is the normal scenario. A default value is defined using the = after the type. Kotlin constructors are bit different than other programming languages. 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. Default Values in the Constructor. But that does not compile. Java by design does not support optional parameters! You can use one another constructor along with the primary constructor in Kotlin. sayHello(last = "Doe") //>Hello Mr Doe Using default parameters in constructors. A constructor is a special kind of function and it is called as soon as the Class object is created. As JPA requires, @Entity classes should have a default (non-arg) constructor to instantiate the objects when retrieving them from the database. class Dog(var breed:String="labrador") : Animal() { } Now if we don’t pass any value for breed it will get “labrador” by default. Note that the compiler only uses the properties defined inside the primary constructor for the automatically generated functions. 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. We are assigning values to color and breed properties. 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