Object declaration syntax in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an object declaration in Kotlin?

An object declaration in Kotlin creates a singleton object, which means only one instance of that object exists throughout the program.

beginner

How do you declare a simple object named Logger in Kotlin?

Use the syntax:

object Logger {
    fun log(message: String) {
        println(message)
    }
}

intermediate

Can an object declaration have properties and functions in Kotlin?

Yes, an object declaration can have properties and functions just like a class, but it cannot have constructors because it is a singleton.

intermediate

What is the difference between an object declaration and a class in Kotlin?

An object declaration creates a single instance automatically (singleton), while a class can have many instances created using constructors.

beginner

How do you access a function inside an object declaration?

You access it directly by the object name, for example: Logger.log("Hello") without creating an instance.

What keyword is used to declare a singleton object in Kotlin?

A instance

B class

C singleton

D object

The keyword object is used to declare a singleton object in Kotlin.

Can an object declaration in Kotlin have a constructor?

A Only secondary constructors are allowed

B Yes, it can have primary and secondary constructors

C No, object declarations cannot have constructors

D Only primary constructors are allowed

Object declarations cannot have constructors because they are instantiated automatically as singletons.

How do you call a function named printMessage inside an object named Notifier?

A printMessage()

B Notifier.printMessage()

C Notifier().printMessage()

D new Notifier().printMessage()

You call the function directly on the object name: Notifier.printMessage().

Which of the following is true about Kotlin object declarations?

A They are instantiated lazily and only once

B They require explicit instantiation

C They can have multiple instances

D They cannot have functions

Object declarations are instantiated lazily and only once, making them singletons.

What happens if you try to create an instance of an object declaration using a constructor?

A It throws a compile-time error

B It creates a new instance

C It creates a copy of the object

D It returns null

Since object declarations have no constructors, trying to instantiate them causes a compile-time error.

Explain how to declare and use an object declaration in Kotlin.

Think about how you create a single shared tool or helper in your program.

Describe the differences between a Kotlin object declaration and a class.

Consider how many copies you want in your program.