Convert to kotlin

Interview.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

/**
 * Convert following class into Kotlin
 */

public class Interview {
    public static void main(String args[]) {
        UserQuestions questions = new UserQuestions();
        questions.printOutNamesWithPrefix(new UserQuestions.NameSuffixDelegate() {
            @Override
            public String addPrefix(TestUser user) {
                String prefix = user.isMale() ? "Mr. " : "Mrs. ";
                return String.format("%s %s", prefix, user.name);
            }
        });
        
        questions.printOutHobbyCount();
    }
}

class UserQuestions {
    private static final TestUser[] users = {
        new TestUser("John", TestUser.GENDER_MALE, "Basketball", "Piano"),
        new TestUser("Joe", TestUser.GENDER_MALE),
        new TestUser("Rachel", TestUser.GENDER_FEMALE, "Basketball", "Running")
    };

    public void printOutNamesWithPrefix(NameSuffixDelegate suffixDelegate) {
        for (TestUser user : users) {
            System.out.println(suffixDelegate.addPrefix(user));
        }
    }

	// Print out all the hobbies from all users and how many times each hobby is entered	
    public void printOutHobbyCount() {
       
    }

    interface NameSuffixDelegate {
        String addPrefix(TestUser user);
    }
}

class TestUser {

    static final String GENDER_MALE = "Male";
    static final String GENDER_FEMALE = "Female";

    public final String name;
    final String gender;
    public final List<String> hobbies;

    TestUser(String name, String gender) {
        this.name = name;
        this.gender = gender;
        this.hobbies = null;
    }

    TestUser(String name, String gender, String... hobbies) {
        this.name = name;
        this.gender = gender;
        List<String> hobbyList = new ArrayList<>(Arrays.asList(hobbies));
        this.hobbies = hobbyList;
    }

    public boolean isMale() {
        return gender.equals(GENDER_MALE);
    }

    public boolean isFemale() {
        return gender.equals(GENDER_FEMALE);
    }
}