Kotlin

Functions

Variables

• Read-only variables with val
• Mutable variables with var
• Top Level Variables
  • Variables can be declared outside the main() function at the beginning of your program.
• It is recommended to declare all variables as read-only by default. Use var only if necessary.
• Variable Declaration with Type Specification
  • val age: Int or val currentProfit: Float

Literals : Numbers, Strings, Characters

• The ability to infer type is called type inference
• Kotlin Basic Types
  • Integers - Byte, Short, Int, Long
  • Unsigned Integers - UByte, UShort, UInt, ULong
  • Floating-point numbers - Float, Double
  • Boolean - Boolean
  • Characters - Char
  • Strings - String

Integer Numbers

• An integer value with lots of digits can have underscores 1_000_000 for better reading
• Even 1_2_3 is valid, but you cannot add _ and start or end of the number
• Kotlin takes Double by default -- to accept float you have to write numbers as .2f etc.

Character

• We wrap a symbol for character in single quote

Strings

• Wrap characters in double quotes instead of single ones

• String Templates

  • print the contents of variables to standard output
  • println("There are ${customers + 1} customers")

Comments

• Three kinds of comments
• End of line comments //
• Multi Line comments /* */
• Documentation Comments ``

Documentation Comments

• Use these kinds of comments to automatically documentation about your source code using a special tool
• These comments are placed above the declarations of respective program elements
• /**
*
*
*
*/
  

Collections

List

• read-only list List \(\rightarrow\) listOf()
• mutable list MutableList \(\rightarrow\) mutableListOf()
• Explicit type specification for lists
  • val age: MutableList<Int> = MutableListOf(1,2,3)
• To prevent unwanted modifications, you can create a read-only view of a mutable list by assigning it to a List. This is also called casting.
• .first() & .last() method

Sets

• Set \(\rightarrow\) setOf()
• MutableSet \(\rightarrow\) mutableSetOf()

Maps

• Map -> mapOf()
  • val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)
  • using to keyword to map key to it's val
• MutableMap -> mutableMapOf()