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Summary - Variables

Combine val, var, const and lateinit to write a profile program.

Summary - Variables

So far you've learned val, var, type inference, const, lateinit and by lazy. val is immutable, var is mutable. The type is usually inferred.

const val is computed at compile-time, lateinit is assigned later, by lazy is computed on first access. Each tool addresses a different deferral need.

Practice Put it together

At the top level, declare const val MULTIPLIER = 2. Inside fun main(), declare var counter = 5, update with counter = counter * MULTIPLIER, and print with println(counter).

Sample solution

Main.kt
const val MULTIPLIER = 2

fun main() {
    var counter = 5
    counter = counter * MULTIPLIER
    println(counter)
}

Expected output

10

Next step

Congratulations! You've completed the variables group. In the next group you'll examine data types in detail: integers (Int, Long), floating-point (Double, Float), Boolean, Char, String and Any/Unit. Each type has a different memory width and use case.

Which type you choose depends on the size and nature of the value. Ready? Let's go.

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which is mutable?

  • val
  • const val
  • by lazy
  • var Correct answer

Explanation: A variable declared with var can be reassigned.

2 Match the concepts

Term Meaning
val Immutable
var Mutable
const val Compile-time
lateinit Assigned later

3 Summary - Variables: fill in the missing part

Question 
var counter = 0
counter ____ 5
Answer 
var counter = 0
counter = 5

Explanation: A var variable is reassigned with =.

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together