KotlinVariables

Kotlin Variables

Variables are containers for storing data values.

To create a variable, usevar orval, and assign a value to it with the equal sign (=):

varvariableName =valuevalvariableName =value

var name = "John"val birthyear = 1975println(name)          // Print the value of nameprintln(birthyear)     // Print the value of birthyear

The difference betweenvar andval is that variables declared with thevar keywordcan be changed/modified, whileval variablescannot.

Variable Type

Unlike many other programming languages, variables in Kotlin do not need to be declared with a specifiedtype (like "String" for text or "Int" for numbers, if you are familiar with those).

To create a variable in Kotlin that should store text and another that should store a number, look at the following example:

var name = "John"      // String (text)val birthyear = 1975   // Int (number)println(name)          // Print the value of nameprintln(birthyear)     // Print the value of birthyear

Kotlin is smart enough to understand that"John" is aString (text), and that1975 is anInt (number) variable.

However, it is possible to specify the type if you insist:

var name: String = "John" // Stringval birthyear: Int = 1975 // Intprintln(name)println(birthyear)

You can also declare a variable without assigning the value, and assign the value later.However, this is only possible when you specify the type:

var name: Stringname = "John"println(name)

var namename = "John"println(name)

Notes onval

When you create a variable with theval keyword, the valuecannot be changed/reassigned.

The following example will generate an error:

val name = "John"name = "Robert"  // Error (Val cannot be reassigned)println(name)

When usingvar, you can change the value whenever you want:

var name = "John"name = "Robert"println(name)

val pi = 3.14159265359println(pi)

Display Variables

Like you have seen with the examples above, theprintln() method is often used to display variables.

To combine both text and a variable, use the+ character:

val name = "John"println("Hello " + name)

You can also use the+ character to add a variable to another variable:

val firstName = "John "val lastName = "Doe"val fullName = firstName + lastNameprintln(fullName)

For numeric values, the+ character works as a mathematical operator:

val x = 5val y = 6println(x + y) // Print the value of x + y

From the example above, you can expect:

• x stores the value 5
• y stores the value 6
• Then we use theprintln() method to display the value of x + y, which is11

Variable Names

A variable can have a short name (like x and y) or more descriptive names (age, sum, totalVolume).

The general rule for Kotlin variables are:

• Names can contain letters, digits, underscores, and dollar signs
• Names should start with a letter
• Names can also begin with $ and _ (but we will not use it in this tutorial)
• Names are case sensitive ("myVar" and "myvar" are different variables)
• Names should start with a lowercase letter and it cannot contain whitespace
• Reserved words (like Kotlin keywords, such as var orString) cannot be used as names