Kotlin: Access specifiers

Access specifiers are used to restrict the data access. Kotlin support 4 access specifiers.

a.   private

b.   protected

c.   internal

d.   public

If you do not specify any access specifier, then public is used by default.

Where can I apply access specifiers?

You can apply access specifiers on Classes, interfaces, constructors, objects, functions, properties and their setter methods. Getters always have the same visibility as the property.

Below table summarizes the access specifiers.

Access Specifier	Description
Private	Members defined with private access specifier are visible only in same scope.
Protected	Members defined with protected access specifier are visible in the same class and all the sub classes of this class.
Internal	Members defined with internal access specifier are visible in the same module.
Public	Members defined with public access specifier are visible from everywhere.

public access specifier

If you mark an element with public modifier, then this element can be accessed from anywhere. If you do not specify any access modifier to an element, the access is public by default.

Test.kt

package com.sample.model

class Test {
 public var i : Int = 10
 var j : Int = 11
}

HelloWorld.kt

import com.sample.model.Test

fun main(args: Array<String>) {
 var obj = Test()

 println("i = ${obj.i}")
 println("j = ${obj.j}")

 obj.i = 88
 obj.j = 99

 println("i = ${obj.i}")
 println("j = ${obj.j}")

}

Output

i = 10
j = 11
i = 88
j = 99

private access specifier

If you declare an element using private access specifier, then the code that is declared in the same scope can access it, no other code can access it.

Test.kt

package com.sample.model

private var totalObjs: Int = 0

class DemoClass1 {
 constructor() {
  totalObjs++
 }

 companion object {
  fun getTotalObjs() = totalObjs
 }
}

class DemoClass2 {
 constructor() {
  totalObjs++
 }
}

HelloWorld.kt

import com.sample.model.*

fun main(args: Array<String>) {
 var obj1 = DemoClass1()
 var obj2 = DemoClass2()

 println("Total objects created : ${DemoClass1.getTotalObjs()}")

 var obj3 = DemoClass1()
 var obj4 = DemoClass2()

 println("Total objects created : ${DemoClass1.getTotalObjs()}")
}

Output

Total objects created : 2
Total objects created : 4

Protected access specifier

Members defined with protected access specifier are visible in the same class and all the sub classes of this class.

Test.kt

open class DemoClass1 {
 protected var i: Int = 10
}

class DemoClass2 : DemoClass1() {
 fun getValueOfI(): Int {
  return i
 }
}

Note

If you override a protected member and do not specify the visibility explicitly, the overriding member will also have protected visibility.

internal access specifier

Members defined with internal access specifier are visible in the same module. A module is a collection of kotlin resources compiled together.

Test.kt

open class DemoClass1 {
 internal var i: Int = 10
}

class DemoClass2 : DemoClass1() {
 fun getValueOfI(): Int {
  return i
 }
}

Note

a.   Local variables, local functions and classes do not have access specifiers

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