What is the difference between 'open' and 'public' in Kotlin?

Question

I am new to Kotlin and I am confused between open and public keywords. Could anyone please tell me the difference between those keywords?

Answer 1

I put here just for my memo, maybe useful for someone else :

open class in kotlin means that a class can be inherited because by default they are not:

 class Car{....}
 class Supercar:Car{....} : // give an error

 open Car2{....}
 class Supercar:Car2{....} : // ok

public class in Java is about the visibility of class (nothing to do with inheritance : unless a class in java is final, it can be inherited by default). In kotlin all the class are public by default.

open method in kotlin means that the method can be overridden, because by default they are not. Instead in Java all the methods can be overridden by default

The method of an open class cannot be overridden by default as usual (doesn't matter if the class is open), they must be declared that they can be overridden :

 open class Car{
    fun steering{...}
 }
 class Supercar:Car{
    override fun steering {...}  // give an error
 } 

 open class Car2{
    open fun steering{...}
 }
 class Supercar:Car2{
    override fun steering {...}  // ok
 }

for more details : https://kotlinlang.org/docs/reference/classes.html