How to check type in Kotlin that's similar to Java instanceof operator

In Java, the instanceof operator is commonly used to check if an Object variable is of a certain type.

You may write code as follows in Java:

class Scratch {
    public static void main(String[] args) {
        Object myVar = "Hello World";
        checkType(myVar);
    }

    private static void checkType(Object myVar) {
        if (myVar instanceof Boolean) {
            System.out.println("myVar is a Boolean object");
        }
    }
}

But Kotlin doesn’t have the instanceof operator.

Instead, it allows you to check on an Object type using the is and !is operators.

Kotlin is and !is operator explained

The is operator allows you to check on a variable type just like instanceof operator.

Here’s an example code in Kotlin:

var myVar: Any = "Hello"

if (myVar is Boolean){
    print("myVar is a Boolean object")
}

Just like in Java, the is operator can also check if the Any object variable you have is of a custom class that you defined in your Kotlin source code.

In the example below, I can check if the variable is of a Dog class type that I have defined previously:

class Dog {
    fun bark(){
        print("Woof!")
    }
}

var myVar: Any = Dog()

if (myVar is Dog){
    print("myVar is a Dog object")
}

Finally, the !is operator is used to check whether an object is not of a certain type:

var myVar: Any = false

if (myVar !is String){
    print("myVar is a not a String object")
}

// similar to 

if !(myVar is String){
    print("myVar is a not a String object")
}

The !is operator is similar to adding an exclamation mark in an is operator check.

You’ve just learned the Kotlin equivalent to the instanceof operator. Well done! 👍