Companion objects as static alternatives in Kotlin - Mini Project: Build & Apply

Using Companion Objects as Static Alternatives in Kotlin

📖 Scenario: Imagine you are creating a simple app that needs to count how many times a certain action happens. You want to keep this count shared across all instances of a class without creating separate copies for each object.

🎯 Goal: You will build a Kotlin class with a companion object that holds a shared counter. You will then write code to increase and display this counter, demonstrating how companion objects act like static members.

📋 What You'll Learn

Create a Kotlin class named ActionCounter

Inside ActionCounter, create a companion object with a variable count initialized to 0

Add a function increment() inside the companion object to increase count by 1

Add a function getCount() inside the companion object to return the current count

Call increment() three times and then print the current count using getCount()

💡 Why This Matters

🌍 Real World

Companion objects let you keep shared data or helper functions inside a class, similar to static members in other languages. This is useful for counters, constants, or factory methods.

💼 Career

Understanding companion objects is important for Kotlin developers to write clean, efficient code that shares data and behavior without unnecessary object creation.

1

Create the Kotlin class with a companion object and count variable

Create a Kotlin class called ActionCounter. Inside it, create a companion object with a variable count initialized to 0.

Kotlin

class ActionCounter {
    companion object {
        // Your code here
    }
}

Need a hint?

Use var count = 0 inside the companion object to hold the shared count.

2

Add increment and getCount functions inside the companion object

Inside the companion object of ActionCounter, add a function increment() that increases count by 1, and a function getCount() that returns the current value of count.

Kotlin

class ActionCounter {
    companion object {
        var count = 0
        // Your code here
    }
}

Need a hint?

Define increment() to add 1 to count. Define getCount() to return count.

3

Call increment three times using the companion object

Call ActionCounter.increment() three times to increase the shared count.

Kotlin

class ActionCounter {
    companion object {
        var count = 0
        fun increment() {
            count++
        }
        fun getCount(): Int {
            return count
        }
    }
}

// Your code here

Need a hint?

Call ActionCounter.increment() exactly three times in main().

4

Print the current count using getCount

Add a println statement to print the current count by calling ActionCounter.getCount().

Kotlin

class ActionCounter {
    companion object {
        var count = 0
        fun increment() {
            count++
        }
        fun getCount(): Int {
            return count
        }
    }
}

fun main() {
    ActionCounter.increment()
    ActionCounter.increment()
    ActionCounter.increment()
    // Your code here
}

Need a hint?

Use println(ActionCounter.getCount()) to show the count.