Kotlin: Primary and Secondary Constructor, and Inheritance

In Kotlin, class can have primary constructor and secondary constructor. Constructors in subclass varies according to their circumstances.


Subclass has no constructor

Add bracket and argument after the base class.

Subclass has only primary constructor
Subclass has only secondary constructor

Don’t write bracket or argument after base class, and secondary constructor must delegate to constructor of the base class.

Subclass has primary and secondary constructors

Subclass secondary constructor must delegate its constructor.

Un-inheritable class

If base class primary constructor is private and it has no secondary constructor, then it is not inheritable. (I haven’t found the way to inherit yet.)