Android Kotlin - Sealed Classes

Response.kt

/**
 * Declaring Response class as sealed class means,
 * It is an Abstract class like in Java. We can have all the features
 * in Sealed class which Abstract class has.
 * In this example, added one property field to sealed class "Tag" and
 * This is overridden in the classes extended to this sealed class.
 * Sealed classes are used to have restricted hierarchy.
 */
sealed class Response {
  open var tag: String = ""
    get() { return "Response" }
}

/**
 * Success class: Used to represent success representation of
 * "Response" type of class
 * This is final class and we can not have any class extending to "Success" class
 * In this example, we have overridden the "tag" property set in the Response sealed class.
 */
data class Success(val body: String) : Response() {
  override var tag: String = ""
    get() { return "Success Response" }
}

/**
 * Error class: Used to represent failure representation of
 * "Response" type of class
 * This is final class and we can not have any class extending to "Error" class
 * In this example, we have overridden the "tag" property set in the Response sealed class.
 */
data class Error(val code: String, val errorMessage: String ) : Response() {
  override var tag: String = ""
    get() { return "Error Response" }
}

/**
 * Timeout class: Used to represent timeout representation of
 * "Response" type of class
 * This is final class and we can not have any class extending to "Timeout" class
 * In this example, we have overridden the "tag" property set in the Response sealed class.
 */
object Timeout : Response() {
  override var tag: String = ""
    get() { return "Timeout" }
}

Test.kt

 val response: Response = Success("Success")
    when(response) {
      is Success  -> println("Passed : "  + response.tag)
      is Error    -> println("Failed : "  + response.tag)
      is Timeout  -> println("Oops : "    + response.tag)
    }