Visibility modifiers
Classes, objects, interfaces, constructors, and functions, as well as properties and their setters, can have visibility modifiers. Getters always have the same visibility as their properties.
There are four visibility modifiers in Kotlin: private, protected, internal, and public. The default visibility is public.
On this page, you'll learn how the modifiers apply to different types of declaring scopes.
Functions, properties, classes, objects, and interfaces can be declared at the "top-level" directly inside a package:
// file name: example.kt
package foo
fun baz() { ... }
class Bar { ... }If you don't use a visibility modifier,
publicis used by default, which means that your declarations will be visible everywhere.If you mark a declaration as
private, it will only be visible inside the file that contains the declaration.If you mark it as
internal, it will be visible everywhere in the same module.The
protectedmodifier is not available for top-level declarations.
note
To use a visible top-level declaration from another package, you should import it.
Examples:
// file name: example.kt
package foo
private fun foo() { ... } // visible inside example.kt
public var bar: Int = 5 // property is visible everywhere
private set // setter is visible only in example.kt
internal val baz = 6 // visible inside the same moduleFor members declared inside a class:
privatemeans that the member is visible inside this class only (including all its members).protectedmeans that the member has the same visibility as one marked asprivate, but that it is also visible in subclasses.internalmeans that any client inside this module who sees the declaring class sees itsinternalmembers.publicmeans that any client who sees the declaring class sees itspublicmembers.
note
In Kotlin, an outer class does not see private members of its inner classes.
If you override a protected or an internal member and do not specify the visibility explicitly, the overriding member will also have the same visibility as the original.
Examples:
open class Outer {
private val a = 1
protected open val b = 2
internal open val c = 3
val d = 4 // public by default
protected class Nested {
public val e: Int = 5
}
}
class Subclass : Outer() {
// a is not visible
// b, c and d are visible
// Nested and e are visible
override val b = 5 // 'b' is protected
override val c = 7 // 'c' is internal
}
class Unrelated(o: Outer) {
// o.a, o.b are not visible
// o.c and o.d are visible (same module)
// Outer.Nested is not visible, and Nested::e is not visible either
}Use the following syntax to specify the visibility of the primary constructor of a class:
note
You need to add an explicit
constructorkeyword.
class C private constructor(a: Int) { ... }Here the constructor is private. By default, all constructors are public, which effectively amounts to them being visible everywhere the class is visible (this means that a constructor of an internal class is only visible within the same module).
For sealed classes, constructors are protected by default. For more information, see Sealed classes.
Local variables, functions, and classes can't have visibility modifiers.
The internal visibility modifier means that the member is visible within the same module. More specifically, a module is a set of Kotlin files compiled together, for example:
An IntelliJ IDEA module.
A Maven project.
A Gradle source set (with the exception that the
testsource set can access the internal declarations ofmain).A set of files compiled with one invocation of the
<kotlinc>Ant task.