Using variables in super constructor

Support
1

In my class constructor I want to pass variables to the super constructor, but I don’t see any way to do this in Kotlin.

For example, how would I accomplish this Java code in Kotlin?

class MyDbHelper extends SQLiteOpenHelper {
    private static final int DATABASE_VERSION = 2;
    static final String DATABASE_NAME = "my.db";

    public MyDbHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
}
2

In Kotlin classes have a primary constructor:

class MyDbHelper(context: Context) : SQLiteOpenHelper(context, "my.db", null, 2)

However, that also means that you have to pass the literal values of your fields to the super class sonstructor or define them outside of the class.

3

The values you pass are not variables, they are constants. In Kotlin you should define them in the companion object. When you do so (even using @JvmField or @JvmStatic), you can use these values in the constructor. That is also how the translator would translate your Java to Kotlin.

4

Thank you @medium and @pdvrieze

5

This does not work in case of objects.

object DBHelper : SQLiteOpenHelper(A_GLOBAL_CONTEXT, DATABASE_NAME, null, DATABASE_VERSION) {
 private const val DATABASE_NAME = "databbase.db"
 private const val DATABASE_VERSION = 2
 // .. some other code 
}

while this works just fine:

class DBHelper : SQLiteOpenHelper(A_GLOBAL_CONTEXT, DATABASE_NAME, null, DATABASE_VERSION) {
 companion object {
  private const val DATABASE_NAME = "databbase.db"
  private const val DATABASE_VERSION = 2
}
 // .. some other code 
}