object vs class
- Kotlin course
- Intermediate
- Lesson 34/116
- 5 min
Learn the difference between object and class.
object vs class
object and class serve different needs. An object declares a singleton with a single instance; it cannot be instantiated and is used directly by name. A class is a template from which many instances can be created.
Example: object Config { val version = "1.0" } has a single Config for the whole app. A class User(val name: String) creates multiple instances like User("Alex"), User("Mia"). Use object when a singleton is needed, class when multiple instances are needed. A wrong choice leads to shared-state pollution.
Using them together
In an application object and class are usually used together. A class represents instances while an object holds shared helpers and configuration.
Example: object Config { val version = "1.0" }; class User(val name: String). User("Alex") creates a separate instance per user, while Config.version holds a single value for the whole app. This separation clarifies state management: instance data goes in a class, global data in an object.
Practice object Config and class User together
Define an object named Config with a val version = "1.0" property. Define a class User(val name: String). In main print User("Alex").name and Config.version on separate lines with println.
Starter code
// Define the Config object
// Define the User class
// print both in mainSample solution
object Config {
val version = "1.0"
}
class User(val name: String)
fun main() {
println(User("Alex").name)
println(Config.version)
}Expected output
Alex 1.0
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the object and class difference
| Term | Meaning |
|---|---|
object Config |
Single instance |
class User |
Multiple instances |
User("Alex") |
New instance |
Config.version |
Access by name |
2 Which is used for configuration that must keep a single instance throughout the app?
- abstract class
- class
- object Correct answer
- interface
Explanation: An object provides a single instance; it suits configuration.
3 Complete object and class together
object Config {
val version = "1.0"
}
class ____(val name: String)object Config {
val version = "1.0"
}
class User(val name: String)Explanation: class User is multi-instance, object Config is single-instance.