Visibility Modifiers

A visibility modifier (a.k.a access modifiers or access specifiers) is a concept not tied to any specific programming language. It is a language keyword that precedes a declaration and defines the scope from where it is visible -thus can be accessed. Visibility Modifiers are modifiers that when appended to a class, interface, property or function in Kotlin, would define where all it is visible and from where all it can be accessed. The setters of properties in Kotlin can have a separate modifier from the property. There are four visibility modifiers in Kotlin

• • • private
    • protected
    • internal
    • public

Private

The declarations marked with the private modifier are visible inside the file/class containing the declaration.

// Visible just inside this file
private const val numberThree = 3

// Visible just inside this file
private class User()
{
    // Visible just inside the user class
    private val numberEight = numberThree.plus(5)
}

// ERROR: numberEight is not accessible outside the User class
private const val numberEleven = numberEight.plus(numberThree)

Private

Protected

The declarations marked with the protected modifier are visible inside the file containing the declaration and subclasses. This modifier is not allowed for top-level declarations.

// Visible inside this file
private const val numberThree = 3
// Visible inside this file
private open class User() {
    // Visible inside the User class and subclasses
    protected val numberEight = numberThree.plus(5)
}
// Visible inside this file
private class Moderator() : User() {
    // Visible inside the Moderator class
    // numberEight is visible because Moderator is a subclass of User
    private val numberEleven = numberThree.plus(numberEight)
}
// ERROR: protected modifier is not allowed for top level declarations
protected const val numberThree = 3
// ERROR: protected modifier is not allowed for top level declarations
protected class Staff()

Protected

Internal

The declarations marked with the internal modifier are visible everywhere in the same module.

// Internal.kt file
// Visible to everyone in the same module
internal const val numberThree = 3

// Visible to everyone in the same module
internal open class User() {
    // Visible to everyone in the same module that has visibility on User
    internal val numberEight = numberThree.plus(5)
}

// SameModule.kt file
// numberThree is visible because this file is in the same module than Internal.kt
// numberEight is visible because this file is in the same module than User
private const val numberEleven = numberThree.plus(User().numberEight)

// DifferentModule.kt file
// ERROR: numberThree is not visible because this file is in a different module than Internal.kt
// ERROR: numberEight is not visible because User() is in a different module than Internal.kt
private const val numberEleven = numberThree.plus(User().numberEight)

Internal

Public

The declarations marked with the public modifier are visible to everyone. public is the default visibility modifier in Kotlin (a declaration without explicit modifier will be public)

// Public.kt file
// Visible everywhere
public const val numberThree = 3
// Visible everywhere
public open class User() {
    // Visible to everyone with visibility on the User class
    public val numberEight = numberThree.plus(5)
}
// Visible everywhere
public class Moderator() {
    // numberEleven is visible to everyone with visibility on the Moderator class
    // numberEight is visible because User is public and numberEight is public
    public val numberEleven = numberThree + User2().numberEight
}

/ AnotherFile.kt file
// numberThree is visible to any other file because it's public
// numberEight is visible to any other file because User and numberEight are public
// numberEleven is visible to any other file because Moderator and numberEleven are public
private const val numberTwentyTwo = numberThree + User().numberEight + Moderator().numberEleven

Public

Questions

I hope the description was understandable and clear. But if you have still questions, then leave me comments below! 😉

Have a nice a day! 🙂

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