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Summary - Enums

Combine enum class and when to write a state machine.

Summary - Enums

In this group you learned to declare an enum class, access constants with entries/valueOf/ordinal, add properties and methods, write exhaustive branches with when and loop over entries.

Now it is time to combine them in a small task: define an enum, print its count and its first constant. This is a small sample of a real choice structure.

Practice Count days and print the first

Define an enum class called Day with MON, TUE, WED, THU, FRI. In main first print Day.entries.size, then Day.entries.first().

Starter code

Main.kt
fun main() {
    // Define a day type; print the count and the first constant
}

Sample solution

Main.kt
enum class Day { MON, TUE, WED, THU, FRI }

fun main() {
    println(Day.entries.size)
    println(Day.entries.first())
}

Expected output

5
MON

Questions and answers

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

1 Fill in the blank: get the order

Question 
val s = Color.GREEN.____
Answer 
val s = Color.GREEN.ordinal

Explanation: ordinal gives the constant's order.

2 Match tool to purpose

Term Meaning
enum class Declaration
entries All constants
when All branches
ordinal Order

3 Which is true about enum constants?

  • Enum constants are mutable
  • Enums only hold numbers
  • Enum constants are fixed Correct answer
  • Enums cannot implement interfaces

Explanation: Each constant is a single object; it does not change after compile.

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