How to Create and Use Static Variables in Kotlin

1. Declare Static Variables in Kotlin
2. Use the Companion Object to Create Kotlin Static Variables
3. Use the @JvmStatic Annotation to Create Kotlin Static Variables

When we declare a variable as static in Java, we can use it in different classes without the need for creating objects. It means that the memory of a static variable is allocated only once.

Since JVM does not allocate memory multiple times to a static variable, they are used for efficient memory management; however, there is no static keyword in Kotlin. So, how do we declare static variables in Kotlin?

This article introduces how we can implement the concept of static variables in Kotlin.

Declare Static Variables in Kotlin

While Kotlin does not have the static keyword, we can still achieve the same memory management efficiency using:

• the Companion object
• the @JvmStatic annotation

We will go through both methods and see examples for implementing Kotlin static variables.

Use the Companion Object to Create Kotlin Static Variables

We can use the companion keyword to create a companion object to help achieve static variables functionality. We need to use the companion keyword before the object.

These objects can access the private members of a class; hence, there is no need to allocate the memory twice. We can use the class’s name to access these members.

Here’s an example of using the companion objects to achieve static functionality in Kotlin.

fun main(args: Array<String>) {
    println("We are accessing a class variable without creating object.\n" + staticExample.privateVar)
}

class staticExample{
    companion object {
        val privateVar = "Hi, you are accessing a static variable."
    }
}

Output:

Click here to check the demo of the example.

Use the @JvmStatic Annotation to Create Kotlin Static Variables

While the companion object members are like static variables in Java, they have a small difference. During the runtime, companion objects are still members of real objects; hence, they can also implement interfaces.

But one way to declare static variables in Kotlin is by using the @JvmStatic annotation. When we use the @JvmStatic annotation while declaring variables, JVM considers them actual static variables.

Here’s an example of using the @JvmStatic annotation to declare a variable.

fun main(args: Array<String>) {
    println("We are accessing a class variable without creating object.\n" + staticExample.privateVar)
}

object staticExample{
    @JvmStatic
    val privateVar = "Hi, you are accessing a static variable."
}

Output:

Click here to check the demo of the example.