Why object declarations create singletons in Kotlin - See It in Action

Why object declarations create singletons

📖 Scenario: Imagine you want to have a single shared resource in your Kotlin program, like a single printer manager that everyone uses. Kotlin's object declaration helps you create such a single shared instance easily.

🎯 Goal: You will create an object declaration in Kotlin and see how it acts as a singleton by accessing it multiple times and confirming it is the same instance.

📋 What You'll Learn

Create an object called PrinterManager with a function printMessage() that prints a message.

Create two variables firstAccess and secondAccess that refer to PrinterManager.

Compare firstAccess and secondAccess to confirm they point to the same instance.

Print the result of the comparison.

💡 Why This Matters

🌍 Real World

Singletons are used in apps to manage shared resources like printers, database connections, or configuration settings where only one instance should exist.

💼 Career

Understanding Kotlin's <code>object</code> singleton pattern is important for Android developers and backend Kotlin programmers to write clean, efficient, and safe code.

1

Create the object declaration

Create an object called PrinterManager with a function printMessage() that prints the text "Printing a document...".

Kotlin

# Your code here

Need a hint?

Use object PrinterManager to declare a singleton object. Inside it, define fun printMessage() that calls println.

2

Access the object twice

Create two variables firstAccess and secondAccess and assign both to PrinterManager.

Kotlin

object PrinterManager {
    fun printMessage() {
        println("Printing a document...")
    }
}

# Your code here

Need a hint?

Assign PrinterManager to both firstAccess and secondAccess variables.

3

Compare the two references

Create a variable areSameInstance that stores the result of comparing firstAccess and secondAccess using ===.

Kotlin

object PrinterManager {
    fun printMessage() {
        println("Printing a document...")
    }
}

val firstAccess = PrinterManager
val secondAccess = PrinterManager

# Your code here

Need a hint?

Use === to check if both variables point to the same object instance.

4

Print the comparison result

Print the value of areSameInstance.

Kotlin

object PrinterManager {
    fun printMessage() {
        println("Printing a document...")
    }
}

val firstAccess = PrinterManager
val secondAccess = PrinterManager

val areSameInstance = firstAccess === secondAccess

# Your code here

Need a hint?

Use println(areSameInstance) to show if both references are the same object.