| Hard Prerequisites |
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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
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 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") }