Sealed class vs Enum class in Kotlin

Both sealed classes and enums in Kotlin are used to represent a fixed set of types, but they serve different purposes and have distinct features.

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1. enum (Enumeration)

An enum is used when you have a finite set of constant values that do not change.

Key Features of enum

✔ Represents fixed constants.
✔ Each enum value is a single instance (singleton).
✔ Can have properties and methods.
✔ Cannot store additional hierarchy (i.e., no subclasses).

Example:

enum class CarType(val speed: Int) {     
	SEDAN(180),     
	SUV(160),     
	SPORTS(250);      
	fun printSpeed() {         
		println("Max speed: $speed km/h")     
	} 
}  

fun main() {     
	val car = CarType.SPORTS     
	car.printSpeed()  // Output: Max speed: 250 km/h 
}

💡 Use enum when you need predefined, fixed constants with optional properties/methods.

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2. sealed class

A sealed class is used when you need to define a restricted class hierarchy, where each subclass represents a specific state or behavior.

Key Features of sealed class

✔ Can have multiple subclasses (unlike enum).
✔ Useful for representing different types of states (e.g., Success, Error).
✔ Can store additional properties for each subclass.
✔ More flexible than enum.

Example:

sealed class Car {
    data class Sedan(val speed: Int) : Car()
    data class SUV(val speed: Int, val offRoad: Boolean) : Car()
    data class Sports(val speed: Int, val turbo: Boolean) : Car()
}

fun carInfo(car: Car) {
    when (car) {
        is Car.Sedan -> println("Sedan speed: ${car.speed} km/h")
        is Car.SUV -> println("SUV speed: ${car.speed}, Off-road: ${car.offRoad}")
        is Car.Sports -> println("Sports car speed: ${car.speed}, Turbo: ${car.turbo}")
    }
}

fun main() {
    val myCar = Car.Sports(300, true)
    carInfo(myCar)  // Output: Sports car speed: 300, Turbo: true
}

💡 Use sealed class when you need to define multiple subclasses with different properties and behavior.

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Key Differences:

Feature	enum ✅	sealed class ✅
Represents fixed set of types?	✅ Yes	✅ Yes
Can have different properties per type?	❌ No (all must have the same)	✅ Yes
Can have methods?	✅ Yes	✅ Yes
Can have multiple instances?	❌ No (each value is a singleton)	✅ Yes (can create multiple instances)
Can extend into subclasses?	❌ No	✅ Yes
Best for?	Fixed constant values	Hierarchical states & polymorphism

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When to Use What?

Use enum when

• You have a finite set of constant values.
• All values have the same properties and behavior.
• Example: Color.RED, LogLevel.ERROR, CarType.SUV.

Use sealed class when

• You need a restricted class hierarchy.
• Each subclass has different properties or behavior.
• Example: Success/Failure states, different UI states in Android.