General Kotlin MCQs

1. Kotlin interfaces and abstract classes are very similar. What is one thing abstract class can do that interfaces cannot?

2. Inside an extension function, what is the name of the variable that corresponds to the receiver object

3. What is the entry point for a Kotlin application?

4. You are writing a console app in Kotlin that processes test entered by the user. If the user enters an empty string, the program exits. Which kind of loop would work best for this app? Keep in mind that the loop is entered at least once

5. You have started a long-running coroutine whose job you have assigned to a variable named task. If the need arose, how could you abort the coroutine? val task = launch { // long running job}

6. You are attempting to assign an integer variable to a long variable, but Kotlin compiler flags it as an error. Why?

7. The function typeChecker receiver a parameter obj of type Any. Based upon the type of obj, it prints different messages for Int, String, Double, and Float types; if not any of the mentioned types, it prints "unknown type". What operator allows you to determine the type of an object?

8. This code does not print any output to the console. What is wrong? firstName?.let { println("Greeting $firstname!")}

9. Which line of code shows how to display a nullable string's length and shows 0 instead of null?

10. In the file main.kt, you are filtering a list of integers and want to use an already existing function, removeBadValues. What is the proper way to invoke the function from filter in the line below? Val list2 = (80..100).toList().filter(_____)

11. Which code snippet correctly shows a for loop using a range to display "1 2 3 4 5 6"?

12. You are upgrading a Java class to Kotlin. What should you use to replace the Java class's static fields?

13. Your code need to try casting an object. If the cast is not possible, you do not want an exception generated, instead you want null to be assigned. Which operator can safely cast a value?

14. Kotlin will not compile this code snippet. What is wrong? class Employee class Manager : Employee()

15. Which function changes the value of the element at the current iterator location?

16. What three methods does this class have? Class Person

17. Which is the proper way to declare a singleton named DatabaseManager?

18. In order to subclass the Person class, what is one thing you must do? abstract class Person(val name: String) { abstract fun displayJob(description: String)}

19. Your function is passed by a parameter obj of type Any. Which code snippet shows a way to retrieve the original type of obj, including package information?

20. Which is the correct declaration of an integer array with a size of 5?

21. You have created a class that should be visible only to the other code in its module. Which modifier do you use?

22. Kotlin has two equality operators, == and ===. What is the difference?

23. Which snippet correctly shows setting the variable max to whichever variable holds the greatest value, a or b, using idiomatic Kotlin?

24. You have an enum class Signal that represents the state of a network connection. You want to print the position number of the SENDING enum. Which line of code does that?

25. You would like to know each time a class property is updated. Which code snippet shows a built-in delegated property that can accomplish this?

26. What is the correct way to initialize a nullable variable?

27. Which line of code is a shorter, more idiomatic version of the displayed snippet? val len: Int = if (x != null) x.length else -1

28. The Kotlin .. operator can be written as which function?

29. In this code snippet, why does the compiler not allow the value of y to change? For(y in 1..100) y+=2

30. This code snippet compiles without error, but never prints the results when executed. What could be wrong? Val result = generateSequence(1) { it + 1 }.toList(); Println(result)

31. You would like to group a list of students by last name and get the total number of groups. Which line of code accomplishes this, assuming you have a list of the Student data class? Data class Student(val firstName: String, val lastName: String)

32. You have an unordered list of high scores. Which is the simple method to sort the highScores in descending order? fun main() { val highScores = listOf(4000, 2000, 10200, 12000, 9030)}

33. Your class has a property name that gets assigned later. You do not want it to be a nullable type. Using a delegate, how should you declare it?

34. You want to know each time a class property is updated. If the new value is not within range, you want to stop the update. Which code snippet shows a built-in delegated property that can accomplish this?

35. Which line of code shows how to call a Fibonacci function, bypass the first three elements, grab the next six, and sort the elements in descending order?

36. You have two arrays, a and b. Which line combines a and b as a list containing the contents of both? val a = arrayOf(1, 2, 3) val b = arrayOf(100, 200, 3000)

37. This code is occasionally throwing a null pointer exception (NPE). How can you change the code so it never throws as NPE? println("length of First Name = ${firstName!!.length}")

38. What is the execution order of init blocks and properties during initialization?

39. What are the two ways to make a coroutine's computation code cancellable?

40. Which statement declares a variable mileage whose value never changes and is inferred to be an integer?

41. What is the preferred way to create an immutable variable of type long?

42. Which line converts the binaryStr, whish contain only 0s and 1s, to an integer representing its decimal value? val binaryStr = "00001111"

43. In a Kotlin program, which lines can be marked with a label

44. All classes in Kotlin inherit from which superclass?

45. You have written a function, sort(), that should accept only collections that implement the Comparable interface. How can you restrict the function? fun sort(list: List): List { return list.sorted()}

46. Kotlin classes are final by default. What does final mean?

47. You have created an array to hold three strings. When you run the code bellow, the compiler displays an error. Why does the code fail? val names = arrayOf(3) names[3]= "Delta"

48. If a class has one or more secondary constructors, what must each of them do?

49. When you can omit constructor keyword from the primary constructor?

50. How many different kinds of constructors are available for kotlin classes?

51. What is the default visibility modifier in Kotlin?