Kotlin Nested classes:- Geniusofstudent

Nested Classes

Classes can be nested in other classes

class Outer {
    private val bar: Int = 1
    class Nested {
    fun foo() = 2
    }
    }

    val demo = Outer.Nested().foo() // == 2

Inner classes

A class may be marked as inner to be able to access members of outer class. Inner classes carry a reference to an object of an outer class:

class Outer {
    private val bar: Int = 1
    inner class Inner {
    fun foo() = bar
    }
    }

    val demo = Outer().Inner().foo() // == 1 

Anonymous inner classes

Anonymous inner class instances are created using an object expression:

window.addMouseListener(object: MouseAdapter() {
    override fun mouseClicked(e: MouseEvent) {
    // ...
    }

    override fun mouseEntered(e: MouseEvent) {
    // ...
    }
    }) 

If the object is an instance of a functional Java interface (i.e. a Java interface with a single abstract method), you can create it using a lambda expression prefixed with the type of the interface:

 val listener = ActionListener { println("clicked") }