Visibility modifiers

Kotlin allows you to enforce symbol visibility via visibility modifiers, which can be placed on symbol declarations.

There are four visibility modifiers in Kotlin: private, protected, internal and public.

public: declarations are visible everywhere.
private: means visible inside this class only (including all its members)
protected: means visible inside this class (including all its members) + visible in subclasses too
internal: modifier are visible everywhere in the same module.

If you don't supply a visibility modifier, you get the default visibility level, which is public.

Java vs Kotlin

In Java, the default modifier is package private, in Kotlin is public.
Java’s package private doesn’t have an equivalent in Kotlin, the closest is internal.
An Outer class does not see private members of its inner class in Kotlin.
If you override a protected member and do not specify the visibility explicitly, the overriding member will also have protected visibility. In Java the visibility is according to the modifier and the default is still public.