How can I avoid a "Primary constructor call expected" in this case?-CodePudding

I've created a Person class and a Student class here in Kotlin:

In line 27, I'm trying to achieve a case where a user can create a "Student" class by providing 4 parameters: FirstName, LastName, Age, and Degree.

I've also written the equivalent code in Java. I'm trying to achieve the Java equivalent code's Secondary Constructor in line 30:

How can I avoid a "Primary constructor call expected" in the Kotlin code?

CodePudding user response：

For your use case you don't even need secondary constructors. You could have optional arguments in the constructor. Like this for example:

open class Person(var firstName: String, var lastName: String, var age: Int? = null) {
    override fun toString() = "$firstName | $lastName | $age"
}

class Student(firstName: String, lastName: String, var degree: String, age: Int? = null) : Person(firstName, lastName, age) {
    override fun toString() = "$firstName | $lastName | $age | $degree"
}

To demonstrate:

fun main() {
    val a = Person("Aaa", "aaA")
    val b = Person("Bbb", "bbB", 20)
    val c = Student("Ccc", "ccC", "degreeC")
    val d = Student("Ddd", "ddD", "degreeD", 21)

    println(a)
    println(b)
    println(c)
    println(d)
}

Output:

Aaa | aaA | null
Bbb | bbB | 20
Ccc | ccC | null | degreeC
Ddd | ddD | 21 | degreeD