object vs class

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.

Exercise 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.

Show example solution

object Config {
    val version = "1.0"
}

class User(val name: String)

fun main() {
    println(User("Alex").name)
    println(Config.version)
}

Test yourself

Match the object and class difference

object Config

Single instance
class User

Multiple instances
User("Alex")

New instance
Config.version

Access by name
Which is used for configuration that must keep a single instance throughout the app?
- abstract class
- class
- object
- interface
Show answer

object — An object provides a single instance; it suits configuration.

Complete object and class together

object Config {
    val version = "1.0"
}

class ____(val name: String)

Show answer

object Config {
    val version = "1.0"
}

class User(val name: String)

Next lesson: Summary - Object declaration

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