What is the difference between open and public in Kotlin?

The main difference between open and public in Kotlin is:

• public is a visibility modifier that allows a class, function, or property to be accessed from anywhere[1][2][3]. It is the default visibility if no modifier is specified.

• open is not a visibility modifier, but rather a modifier that allows a class or member to be overridden in subclasses[1][2][4]. By default, classes, functions and properties in Kotlin are final and cannot be overridden, unless marked as open.

In summary:

• public controls the visibility and accessibility of a declaration
• open controls whether a class or member can be overridden in subclasses

For example:

open class Base {
    open fun foo() { ... }
}

class Derived : Base() ...