How to create an instance of anonymous class of abstract class in Kotlin?
From the official Kotlin language documentation:
window.addMouseListener(object : MouseAdapter() { override fun mouseClicked(e : MouseEvent) { // ... }
Applied to your problem at hand:
val keyListener = object : KeyAdapter() { override fun keyPressed(keyEvent : KeyEvent) { // ... }
As Peter Lamberg has pointed out - if the anonymous class is actually an implementation of a functional interface (i.e. not of an abstract class), SAM Conversions can be used to simplify this statement even further:
val keyListener = KeyAdapter { keyEvent -> // ...}
Please also note this discussion about the different usage of interfaces defined in Java and Kotlin.
In Java
private Comparator<Integer> comparator = new Comparator<Integer>(){ @Override public int compare(Integer o1, Integer o2) { return o1.compareTo(o2); }};
in Kotlin
private val comparator = object: Comparator<Int> { override fun compare(o1: Int, o2: Int): Int { return o1.compareTo(o2) }}
But because Comparator is a FunctionalInterface we can take advantage of SAM conversions and write
private val comparator = Comparator<Int> { o1, o2 -> o1.compareTo(o2) }
Please note that SAM feature only works for Functional
interfaces defined in java, if you need to create object
of a kotlin interface
with single method then you will have to use object
syntax.