What are the differences between data classes and sealed classes in Kotlin?

Data classes in Kotlin are designed for storing data. They automatically generate useful methods like equals(), hashCode(), toString(), copy(), and componentN().

Sealed classes are used to represent a restricted class hierarchy. All subclasses of a sealed class must be declared in the same file. This allows the compiler to check all possible subtypes when using when expressions, ensuring exhaustiveness.

Main differences:

Attribute	Data class	Sealed class
Purpose	Data storage	Restricted class hierarchy
Methods	Auto-generated	Not auto-generated
Subclasses	Can be anywhere	Restricted to same file
Usage	Like POJO (Plain Old Java Object)	To represent finite states
Abstract	Cannot be abstract	Can be abstract

Example of data class:

// Data class
data class User(val name: String, val age: Int)

Example of sealed class:

// Sealed class
sealed class Result {
    data class Success(val data: String) : Result()
    data class Error(val code: Int, val message: String) : Result()
    object Loading : Result() // Singleton object
}