What are the main differences between classes declared with the keywords sealed and abstract?

Main differences between sealed and abstract classes in Kotlin:

• Inheritance:

  • sealed class restricts subclasses — all subclasses must be declared in the same file as the sealed class itself.
  • abstract class does not restrict inheritance — subclasses can be declared anywhere.

• Usage:

  • sealed classes are convenient for representing a limited set of options (e.g., for when expressions without else).
  • abstract classes are used to create base classes with partial implementation.

• Instantiation:

  • Neither class can be instantiated directly.

Example of using a sealed class:

sealed class Result {
    data class Success(val data: String) : Result()
    object Error : Result()
}

fun handle(result: Result) = when(result) {
    is Result.Success -> println("Data: ${result.data}")
    Result.Error -> println("Error occurred")
}