Intro To Kotlin

Prepare for Project Preparation Using Ecilipse IDE and Kotlin Marketplace Extension

Learn Kotlin: https://kotlinlang.org/docs/reference

This is only my note during learning and coding something may be mistake.

Theethawat Savastham | Student at Prince of Songkla University Hatyai Thailand (At first I cannot typing in Thai in Ecilipse IDE) Now I learn in IntelliJ IDEA it can type in Thai but I'm idle.

Structure

• Don't Need a Pre-processor because Kotlin is initial itself at the begining from IDE
• Don't worry about package name, It nescessory only to show that it are in the same domain. In file system they don't show in class view but in IDE it will show you the structure of class
• Function Initial run with main
• No Semicolon needed in Kotlin

Table of Content

• Basic Syntax
• Function
• Variable
• String Management
• Array
• Class

Basic Syntax

printing out the word

//using print or println
print("Hello World")

printing out the value of variable

It can be inside the double quote with $ sign using variable Name

print(" $variablename ")
//If have any calculating
print(" ${variableName1 + variableName2}")

Function

• To call using like in C Language
• Using fun to initial the function

Function Prototype

fun functionName(parameterName:ParameterType): Returntype{
}

Example for Very Basic Function (don't have return)

fun sum(a:Int,b:Int){
	println("a is $a  b is $b")
}

Call function to use Return Value

In variable define or redefine

	var x = functionName(Parameter)
	var y:Int
	y = functionName(Parameter)

Beware Function and Properties are not the same

Using the properties

In Properties we use to get something from variable you can using Kotlin Library properties

• Calling Properties

	var testLengthVariable = "Theethawat"
	var theethawatLength ="Theethawat".length

• Or calling in print statement

	println("Variable of testLengthVariable is ${testLengthVariable.length}")

Variable

• Using val can be assign a value only once
• Using var can be reassign
• Can use both Type define or not, if you not define a type you must initial value in the declare variable part and Kotlin will assign the type automatically
• Type Define and value Define is optional All are correct

var a:Int =1
var a = 2
var a:Int

• This is example that Incorrect

var a 

• Variable can define both in global and local (Private to function) if it be global it can be modify by any function without re parameter-initial like

var x = 0
fun incrementX() { 
   x += 1 
}

String Management

Triming Margin

Can use trimMargin using with prefix '|' only if use another prefix using trimMargin('Prefix')

val str3 = """ #Hello World""".trimMargin()
val str4 = """ #Hello World """.trimMargin("#")

Can use .trimIndent for trim white space before text like a white space and Can use triple quote """ for let string in the string can be multiple line as we code

Array

Array Declaring

Can Creating Array with Initial Value , Initial Value Using Function or Uninitialized using normal form arrayOf if you initial value

val a = intArrayOf(11,13,15,17,12)

or using Specific type of Array

• BooleanArray booleanArrayOf(true, false)
• ByteArray byteArrayOf(1, 2, 3)
• CharArray charArrayOf('a', 'b', 'c')
• DoubleArray doubleArrayOf(1.2, 5.0)
• FloatArray floatArrayOf(1.2, 5.0)
• IntArray intArrayOf(1, 2, 3)
• LongArray longArrayOf(1, 2, 3)
• ShortArray shortArrayOf(1, 2, 3)

or can design array by using function like

val asc = Array(5,init = {i->i+1})
 for (b in asc){
     println(b)
 }

Array Properties

• Properties that can use when declare an Array sortedArray(), sortedArrayDescending()

• Properties that can use when we using function sort(), sortDescending() , min(), max(),first(), last() it will return a view of the things that you want in array (some only for Int or Number Variables) for example

  println("List of Array B is ${b.sorted()}")
  

Collection

Collection is like array but it's the tool that can easier management

• List use Listof() (Can replace string with other type)

  val  myList = listOf<String>("Theethawat","Songpon")
  

• Map use mapOf()

   val myMap = mapOf<Int,String>(Pair(1,"Theethawat"), Pair(2,"Theematach"))
  

• Set use setOf()

  val mySet = setOf<String>("Theethawat","Sirinuch")
  

  using 3 types of collection and other type of Array can be random access

Class

Basic Concept of Class

• It's like class in Java and sometime it's like stucture in C in my own opinion
• Use function (main or any) to call a class
• If Compare to Java it has 3 part
  • Field for variable declare and initial (Java divide into field and Constructor) and can use argument also() to make this variable call the function like val nameInput = "The Input value is $name".also(::println)
  • init() can use for initial, set value and call function in class
  • function fun()
• Everythings contain public, protected, private same like other OOP
• Can use dot(.) for go to the attribute like in C or Java
• For Example in file Address.kt

Object

Companion object

If your class have a Companion object show that you can implement or adding the function to that object like

class MyClass {
	companion object { }  // will be called "Companion"
	}

	fun MyClass.Companion.printCompanion() { println("theethawat") }

	fun main() {
	MyClass.printCompanion()
	} 

You will got an output "Theethawat", i pick it from official Document at Object Documents in Kotlin

Basic Function and library

• Kotlin will add Basic Library name kotlin.* if you use IDE or compiler
• There include many function inside
• String Function Reference is located at https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-string/index.html