Create a mutable list in the getMutableList function and return the list, as follows:

fun getMutableList() : MutableList<Int> {
    val list = mutableListOf(1,2,3,4,5)
    return list
}

Create a listFromKotlin variable in Java and assign a list to this variable by using the CallKotlinKt.getMutableList function from Kotlin.

See the following example:

public static void main(String args[]) {

    System.out.print("Kotlin mutable list");
    //List<int> listFromKotlin = KotlinToJavaKt.mutableList();

    List<Integer> listFromKotlin = CallKotlinKt.getMutableList();
    listFromKotlin.add(6);
    for (int i = 0; i < listFromKotlin.size(); i++) {
        System.out.println("Element " +  listFromKotlin.get(i));
    } 
}

Notice that Kotlin is not familiar with primitive data types. As a result, we must provide a list of Integer classes:

//List<int> listFromKotlin = KotlinToJavaKt.mutableList(); // list of int
List<Integer> listFromKotlin = CallKotlinKt.getMutableList(); // List of Integers