In Kotlin, we can also declare a specific type of variable with var variableName : nameOfDataType type annotation:

var myInteger : Int
var myString : String
val myDouble : Double

Once the variables are declared, we can assign values to them:

myInteger = 10
myString = "Hello"
myDouble = 12.123

Having variable declarations with explicit data types and assigning a value at the same time is also possible:

val myInt : Int = 10
var myString : String = "Hello"

Variable declaration and initialization is explained in the following example:

fun main(args: Array<String>) {
    var myName: String // Variables can be initialized explicitly
    myName = "Jon" // Initialization
    // declaration and initialization in one line
    var myInt: Int = 10
    var myLong: Long = 11
    var myShort: Short = 11
    var myByte: Byte = -128
    var d1 = 5.10 // Declaration of Double and Float
    var d2: Double = 5.10
    var f1 = 5.10
    var f2: Float = 5.10f
}

Kotlin data types are divided into the following groups:

• Number data types 
• Real data types
• Boolean data types 
• Character data types

Now let's have a look at each category in the following sections.