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Summary - Kotlin basics

Combine main, println and comments to write your first Kotlin program.

Summary - Kotlin basics

So far you've learned the structure of a Kotlin program, writing to the screen, comments and string templates. A Kotlin program starts with fun main(), writes with println(...), adds comments with // and /* */, and embeds variables in strings with $.

These concepts will be the foundation for all following lessons. Let's combine them in a short exercise.

Practice Put it together

Write a fun main(). Inside it, in order: a single-line comment, val name = "Alex", and println("Hello $name").

Sample solution

Main.kt
fun main() {
    // start
    val name = "Alex"
    println("Hello $name")
}

Expected output

Hello Alex

Next step

Congratulations! You've completed the Kotlin basics. In the next group you'll dig into variables: the difference between val and var, type inference, const, lateinit and by lazy.

Each lesson adds a new concept with a short exercise. You'll practice declaring variables, annotating types and assigning values. 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 Kotlin's program entry point?

  • fun start
  • fun main Correct answer
  • fun run
  • fun begin

Explanation: fun main is the entry point of a Kotlin program.

2 Match the concepts

Term Meaning
fun Function
println Print
// Comment
$ Template

3 Summary - Kotlin basics: fill in the missing part

Question 
val name = "Alex"
println("Hello $____")
Answer 
val name = "Alex"
println("Hello $name")

Explanation: You embedded the variable with $name.

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