Sealed vs Enum vs Abstract · Sealed Classes and Interfaces in Kotlin | Kotlin

Sealed vs Enum vs Abstract

Which One?

	enum class	sealed class / interface	abstract class / open
Set of subtypes	fixed constants	fixed subclasses	open to anyone
Instances per case	exactly one	many (or one with object)	many
Different data per case	no (same properties)	yes	yes
Exhaustive when	yes	yes	no (needs else)
Example	Direction, Plan, OrderStatus	UiState, Result, NetworkError	BaseActivity, Account

Same Idea, Two Ways

Example

Use an enum when cases carry no extra data; switch to sealed types when they do.

enum class ConnectionType { WIFI, MOBILE, NONE }

sealed interface Connection {
    data class Wifi(val ssid: String) : Connection
    data class Mobile(val network: String, val signalBars: Int) : Connection
    data object Offline : Connection
}

fun describe(c: Connection) = when (c) {
    is Connection.Wifi -> "Wi-Fi: ${c.ssid}"
    is Connection.Mobile -> "${c.network} with ${c.signalBars} bars"
    Connection.Offline -> "No internet"
}

fun main() {
    println(ConnectionType.entries)
    listOf(Connection.Wifi("Home_5G"), Connection.Mobile("Jio 5G", 3), Connection.Offline)
        .forEach { println(describe(it)) }
}

Output

[WIFI, MOBILE, NONE]
Wi-Fi: Home_5G
Jio 5G with 3 bars
No internet