Kotlin Variable
3. Kotlin Variable
3.1 Variable Declaration
3.2 Difference between val and var
3.3 Top level variable
These are some useful features of Kotlin variables-
- In Kotlin, the variable can start with a letter, $ and _.
- The variable names can contain letters, digits, underscores, and dollar signs.
- The variable names are case sensitive.
- Using equal to (=) assignment operator, we can assign a value to a variable.
Variable Declaration
A variable is a name or symbol that contains a value. We assign a value to a variable and that variable becomes reference to the assigned value.
In Kotlin, there are two keywords for declaring variables, val and var.
Example
fun main(args : Array<String>) {
var x = "Tiger"
val y = "Cow"
println("$x and $y")
}
In the above example, both var and val variables are of type string. It does not necessary to declare the variable type. But we can specify them, like -
fun main(args : Array<String>) {
var x: String = "Tiger"
val y: String = "Cow"
println("$x and $y")
}
Output
Tiger and Cow
Difference between val and var
The var is equivalent to declaring a variable in Java, it is a mutable variable, which can be changed to another value by reassigning it. But, val is an immutable variable or read only variable which cannot be changed later in the program once the value is assigned. They can be assigned a value only once. This is similar to the final variable of Java.
We can reassign the value of variable declared using var, but we cannot reassign the value of variable declared using val.
Example
fun main(args : Array<String>) {
var x: String = "Tiger"
x = "Lion" //valid
val y: String = "Cow"
y = "Dog" // error
println("$x and $y")
}
The above program returns the following error -
Error:(5,5) Kotlin: Val cannot be reassigned.
Top level variable
The variable used in function defined at the top level.
Example
fun main(args : Array<String>) {
var x: String = "Tiger"
fun wild() {
println("$x is wild animal.")
}
wild()
}
Tiger is wild animal.