Calling primary constructor from secondary constructor after some calculations are done-CodePudding

Basic question. I have a primary and secondary constructor, and inside the secondary constructor I calculate/fetch the primary constructors

This is an issue since as far as I am aware you need to immediately call the primary constructor inside the second.

Like so

constructor() : this(/*parameters for primary constructor*/)

However, I can't call the primary constructor because I don't know the parameters yet.

constructor() : this(/*???*/) {
   //find parms of primary constructor
   //i want to call primary constructor here
}

Is it possible to call the primary constructor later on in the secondary constructor?

Is there a better way to structure this to avoid the issue?

Here is an oversimplified example

class Test(var name: String,var age: String,var dateOfBirth: String){
    constructor(id: String) : this(/*???*/) {
      //get name, age, dob, from id

      I want to call the primary constructor here since 
    }
}

My best solution was simply to send empty/null values to the primary constructor and then change them in the body of the constructor

constructor(id: String) : this(null,0,null) {
   name = 
   age = 
   dateOfBirth = 
}

This works, but I was wondering if there is a better way

It is a definite possibility there is just a far better way to structure this whole thing, that would avoid this issue altogether, so let me know if that is the case!

CodePudding user response：

You should avoid using any calculations inside of a constructor. This is a bad practice in general. My suggestion for you is to use builder functions. Something like:

class Test(
    var name: String,
    var age: String,
    var dateOfBirth: String) {
    companion object {
        fun fromId(id: Long): Test {
            //calculations
            return Test("", "", "")
        }
    }
}

CodePudding user response：

You do not need it all. Declare variables in top level of class and set values after they are calculated.

class Sample(val n: Int, val m: Int) {
    private val sum: Int

    init {
        sum = n   m
    }
}

Then every time you initialize the class, the value of your variable will be calculated