We can also call the Kotlin singleton class in Java. Let's create a singleton class in Kotlin by using the object keyword:

object Singleton {
    fun happy() { 
        println("I am Happy")
    }
}

Furthermore, we can call the Singleton class and the happy function in Java by using the INSTANCE keyword:

public static void main(String args[]) {
    Singleton.INSTANCE.happy();
}

Notice that we do not need to use a Kotlin filename as a reference, but the object class name, Singleton, is sufficient. We can skip the INSTANCE keyword as well. Add the @JvmStatic annotation at the beginning of the function signature:

object Singleton {

    fun happy() {
        println("I am Happy")
    }

    @JvmStatic fun excited() {
        println("I am very Excited")
    }
}

Once this is done, call the excited function directly without using the INSTANCE keyword in Java:

public static void main(String args[]) {
    Singleton.INSTANCE.happy();
    Singleton.excited();
}

Execute the Java program and verify the output, as follows:

I am Happy
I am very Excited