Kotlin Visibility Modifiers

In this article, you will learn about4There are several visibility modifiers, as well as how they work in different situations.

Visibility modifiers are keywords used to set the visibility (accessibility) of classes, objects, interfaces, constructors, functions, properties, and their setters. (Visibility modifiers cannot be set for getters, as they always have the same visibility as the property)

InKotlin Classes and ObjectsIn this article, you have briefly learned about the visibility modifiers public and private. In this article, you will learn in detail about the other two visibility modifiers protected and internal (as well as public and private).

Visibility modifiers within a package

A package organizes a group of related functions, properties, and classes, objects, and interfaces.

Note:If no visibility modifier is specified, the default is public.

Let's take an example:

//File name: hello.kt
package test
fun function1() {}　　　//Public by default and visible everywhere
private fun function2() {}　　　//Visible within hello.kt
internal fun function3() {}　　　//Visible within the same module
var name = "Foo"　　　//Everywhere
　　　　get() = field　　　//Visible within hello.kt (same as its properties)
　　　　private set(value) {　　　//Visible within hello.kt
　　　　　　　　field = value
　　　　{}
private class class1　{}　　　//Visible within hello.kt

Visibility modifiers within classes and interfaces

The following is how visibility modifiers work for class-level declarations (functions, properties):

Note:If you override a protected member in a derived class without specifying its visibility, its visibility will also be protected.

Let's take an example:

open class Base() {
　　　　var a =　1　　　　　　　　　　　　　　　　　//Public by default
　　　　private var b =　2　　　　　　　　　//　Base class is private
　　　　protected open val c =　3　　//Visible to Base class and Derived class
　　　　internal val d =　4　　　　　　　　//Visible within the same module
　　　　protected fun e() { }　　　　　//Visible to Base class and Derived class
{}
class Derived: Base() {
　　　　//　a, c, d, and e() All properties of Base class are visible
　　　　//　b is not visible
　　　　override val c =　9　　　　　　　　//　c is protected
{}
fun main(args: Array<String>) {
　　　　val base = Base()
　　　　//base.a and base.d are visible
　　　　//　base.b, base.c and base.e() are not visible
　　　　val derived = Derived()
　　　　//　derived.c is not visible
{}

Change the Visibility of the Constructor

By default, the visibility of the constructor is public. However, you can change it. To do this, you need to explicitly add the constructor keyword.

In the following example, the constructor is set to public by default:

class Test(val a: Int) {
　　　　//　code
{}

You can change its visibility by the following methods.

class Test private constructor(val a: Int) {
　　　　//　code
{}

Here, the constructor is private.

Note: 　In Kotlin, local functions, variables, and classes cannot have visibility modifiers.