Kotlin is operator examples | Check variable is of an instance type

This tutorial explains how to check the variable type or instance of a class in Kotlin with examples.

Sometimes, developers need to check the runtime type of a class in Kotlin, and Kotlin provides the is operator for this purpose.

#What is the ‘is’ operator in Kotlin?

The is operator is used to check if a given variable type is an instance of a specified class type. This is very helpful for developers to determine the type of an object at runtime.

is operator syntax

variable is class

Here, variable is a Kotlin valid variable declared with either a primitive or custom class type. Possible variable values include variables, object variables, and strings.

fun main() {
 val msg = "Cloudhadoop";
 println(msg is String) // true
    val num=123;
    println(num is Int) // true
}

#Kotlin Check class name as an string

Kotlin provides class literal syntax to get the name using reflection.

variable::class returns an class name

• variable::class.java.typeName: returns java class type name
• variable::class.simpleName: Returns just the class name
• variable::class.qualifiedName: It returns Kotlin Class Name.

Syntax:

variable::class.simpleName
variable::class.qualifiedName
variable::class.java.typeName

Here is an example

fun main() {
    val msg = "Cloudhadoop";
    println(msg::class.java.typeName)
    println(msg::class.simpleName);
    println(msg::class.qualifiedName);

    val num=123;
    println(num::class.java.typeName)
    println(num::class.simpleName);
    println(num::class.qualifiedName);
}

Output:

java.lang.String
String
kotlin.String
int
Int
kotlin.Int

#Kotlin Check variable is of interface or class

The is operator checks whether a given variable implements an interface or is an instance of a class.

interface Animal {
    fun eat()
}
class Lion : Animal {
    override fun eat() {
    }
}

fun main() {
    val lion = Lion()
    println(lion is Animal)
    println(lion is Lion)

    println(lion::class.java.typeName)
    println(lion::class.simpleName);
    println(lion::class.qualifiedName);

}

Output:

true
true
Lion
Lion
Lion

#Conclusion

In conclusion, this tutorial provides a step-by-step example for checking the type of a variable or instance in Kotlin using the is operator. It covers examples for primitive types, interfaces, and custom classes.