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