Sealed classes
If you have experience with C#, then the sealed keyword might be confusing to you. C# uses the sealed keyword to prevent inheritance from a class, the same way Java uses final when declaring a class. Sealed classes in Kotlin are used to define restricted class hierarchies.
Sealed classes are similar to enum classes; you use them to define a fixed set of options. But unlike enum classes, where each constant is a single instance, sealed classes can have multiple instances for each option.
This restricted class hierarchy can be really useful when used with when expressions.
Here's an example of a sealed class hierarchy used with a when statement:
sealed class SuperHero
class Hulk: SuperHero() {
fun smashOpponent() {
}
}
class SuperMan : SuperHero() {
fun flyToKrypton() {
}
}
class SpiderMan : SuperHero() {
fun useSpiderSense() {
}
}
fun actOnHero(hero: SuperHero) {
when (hero) {
is Hulk -> {
hero.smashOpponent()
}
is SuperMan -> {
hero.flyToKrypton(...