InnerClass.kt

package readinglist

class DirectoryExplorer(val user:String){

    inner class PermissionCheck(){
        fun validatePermission(){

        }
    }

    fun listFolder(folder:String, user:String){
        val permissionCheck = PermissionCheck()
        permissionCheck.validatePermission()

    }
}

fun main(args: Array<String>) {
     val dir = DirectoryExplorer()
    val pc = DirectoryExplorer().PermissionCheck()

}

NestedClass.kt

package readinglist

class DirectoryExplorer(){

    class PermissionCheck(){
        fun validatePermission(user:String){

        }
    }

    fun listFolder(folder:String, user:String){
        val permissionCheck = PermissionCheck()
        permissionCheck.validatePermission(user)

    }
}

fun main(args: Array<String>) {
     val dir = DirectoryExplorer()
    val pc = DirectoryExplorer.PermissionCheck()

}

//kotlin allows me to access nested classes
//If i dont want to i can declare nested class as private

//we can access this nested class from java too
//DirectoryExplorer.PermissionCheck pc = new DirectoryExplorer.PermissionCheck()

//Now what if i want to access property of external class in nested class
//which is not possible by default . In order to do so define the nested class as
//a inner class
//but then i cant access nested class as DirectoryExplorer.PermissionCheck()
//since now nested class has becoome pasrt of the external class insatnce
//hence we would have to do DirectoryExplorer().PermissionCheck()

//kotlin allows me to access nested classes
//If i dont want to i can declare nested class as private

//we can access this nested class from java too
//DirectoryExplorer.PermissionCheck pc = new DirectoryExplorer.PermissionCheck()

//Now what if i want to access property of external class in nested class
//which is not possible by default . In order to do so define the nested class as
//a inner class
//but then i cant access nested class as DirectoryExplorer.PermissionCheck()
//since now nested class has becoome pasrt of the external class insatnce
//hence we would have to do DirectoryExplorer().PermissionCheck()