Sealed Class VS Enum Class

22 Jun 2024 . kotlin .

Sealed Class

Sealed classes provide a hierarchy of classes that have subclasses that we can only declare at compile time.

sealed class OsSealed(val releaseYear: Int = 0, val company: String = "") {
    constructor(company: String) : this(0, company)

    object Linux : OsSealed("Open-Source") {
        fun getText(value: Int): String {
            return "Linux by $company - value=$value"
        }
    }

    object Windows : OsSealed("Microsoft") {
        fun getNumber(value: String): Int {
            return value.length
        }
    }

    object Mac : OsSealed(2001, "Apple") {
        fun doSomething(): String {
            val s = "Mac by $company - released at $releaseYear"
            println(s)
            return s
        }
    }

    object Unknown : OsSealed()

    fun getTextParent(): String {
        return "Called from parent sealed class"
    }
}

Enum Class

We use an enum class to relate each enum constant with its parent.

enum class OsEnum(val releaseYear: Int = 0, val company: String = "") {
    Linux(0, "Open-Source") {
        override fun getText(value: Int): String {
            return "Linux by $company - value=$value"
        }
    },
    Windows(0, "Microsoft") {
        override fun getText(value: Int): String {
            return "Windows by $company - value=$value"
        }
    },
    Mac(2001, "Apple") {
        override fun getText(value: Int): String {
            return "Mac by $company - released at $releaseYear"
        }
    },
    Unknown {
        override fun getText(value: Int): String {
            return ""
        }
    };

    abstract fun getText(value: Int): String

    fun getTextParent(): String {
        return "Called from parent enum class"
    }
}

Sealed Class vs Enum

In a sealed class, we can simply add multiple custom constructors depending on what we need. Furthermore, we can define multiple functions with different names, parameters, and return types.
In an enum class, we can’t define different functions in each enum constant. Therefore, we had to implement a method that we didn’t need for that constant.