This document outlines a Kotlin study group presentation on variables, constants, types, and conditionals. The presentation covers declaring and initializing variables with val and var, built-in types, constants, if and when conditionals, statements vs expressions, inspecting Kotlin bytecode, ranges, and string templates. The presenter is John, an Android developer at Rakuten Viki who has 2 years of experience using Kotlin.

1. Variables, Constants, Types, and
Conditionals
Kotlin Study Group
John

2. Hi, I am John
- Android Developer
- Work on Rakuten Viki
- Use Kotlin for 2 years
- Linkedin:
https://www.linkedin.com/in/chang-john-0a95237a/

3. Outline
- What’s the structure of declaring a variable?
- Val v.s Var
- Constants
- Conditionals
- If keyword
- When keyword
- Statement and Expression
- Supplement
- Inspecting Kotlin Bytecode
- Range
- String templates
- Q&A

4. What’s the structure of declaring a variable?
var experiencePoints: Int = 5
val playerName: String = “Estragon”
val name = “Madrigal”
var healthPoint = 100
var name: String
Why type can ignore? Because of type inference

5. Built-in types

6. Val v.s Var
Var usage
Val usage
Once variable is declared by val, it is read-only
variable
Once variable is declared by var, it is able to be
modified variable
We recommend that you use a val any time you do not need a var.

7. Why need to distinguish var and val?
- Almost all of cases on production, value(data) is decided already when variable is
declared.
For example, get response from backend or get information from database,
generate financial report...
- Avoid others to destroy your design
For example, data class Person(val id: Int, val name: String)
val p1 = Person(“123456789”, “John”)
p1.name = “Johnny”

8. What are benefits using val often? [Advanced]
- When you need the variable, you just declare.
- Due to feature of val is ready-only, you can track origin first on debug(easy
debug)
- Due to variable by val must assign value while you declare and disallow be
modified, you will build constructor-injection architecture unawarely(easy
testing)
- According to above benefits, you will build a clear(immutable) codebase to
decrease software complexity(easy maintain)

9. Compile-Time Constant
Cannot exist ‘const’ only
Cannot correspond with ‘var’ keyword
Cannot enclose on function
Cannot declare non primitive type

10. Compile-Time Constant
Success - const is used for non-enclosed block(function, class) and primitive type
Primitive Type: String, Int, Double, Float, Long, Short, Byte, Char, Boolean

11. Conditionals - If keyword
One line if expression so
that remove braces
Append comparison
and logical operators
comparison
logical
Support nested

12. Conditionals - when keyword

13. Conditionals - statement and expression
This is a statement This is an expression

14. What’s different when i use the expression?
- Code become more straightforward
statement expression

15. What’s different when i use the expression?
- Code become more exhaustive
statement expression

16. Inspecting Kotlin Bytecode

17. Inspecting Kotlin Bytecode
Kotlin Java

18. Range
Ctrl + Shift + P can understand its type

19. String template

20. String template

21. Q&A