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Creating Variables and Methods in Kotlin

Variables​

All programming languages involve variables. Think of a variable like a parking space. A car can enter the parking space, while it's there you can interact with the car, and the car can leave and be replaced by a new one. Variables are parking spaces for data. They offer us the ability to store and manipulate data.

In Kotlin, a variable is declared using a name and some value.

The structure is as follows:

var + (the name of the variable) + = + (the value)

var myVariable = 10

In Kotlin, the var keyword allows the variable to be changed. But if we don't want the variable to be changed after we created it, we can replace it with the val keyword, which makes the variable read-only.

tip

Kotlin is a statically-typed language. This means that when you declare a variable, you have to tell Kotlin what kind of data you want to store in the variable. This is called a data type.

Data Types​

Kotlin needs to know what kind of data we want to put in our variables. A data type basically provides Kotlin with information so it knows what the variable actually means. There are 4 main built-in data types in Kotlin: String, Int, Double, Boolean.

String is for words and letters. They are created by surrounding the content in double-quotes (")

var myString = "Hello, World!"

Int is for integer numbers (numbers without a decimal point).

var myInteger = 36

Double is for real numbers (numbers with a decimal point).

var myDouble = 12.5

Boolean is for true or false values.

var myBoolean = true
tip

Kotlin has a unique feature where it can automatically determine the data type of a variable. However, understanding data types is still important because once we set the data type of a variable, it cannot be changed.

Functions​

Functions are ways to have pieces of code that can be reused in other places. In math, we write functions like this:

f(x) = 2x + 5

In Kotlin, functions exist similarly. They have a name, can take in inputs, and can return some value. To write a function, we write the special fun keyword, then the name of the function, its inputs, and the function body.

The inputs to the function are called parameters. In Kotlin, we write the parameters by writing the name of the parameter, a colon (:), and the data type of the parameter. At the end of the paramaters, we also need to add a colon(:) and our return type, or nothing if we don't want to return anything.

To return some value from the function, we simply write return and then the value that we want to return. At the end of the paramaters, we also need to add a colon(:) and our return type, or nothing if we don't want to return anything.

Here is a sample function in Kotlin.

fun add(a: Int, b: Int): Int {
    return a + b
}

Naming Rules​

When using functions or variables in Kotlin, there are some restrictions for how we name things.

  • No spaces
  • Cannot start with a number
  • Cannot contain a special character
  • The first letter should always be lowercase

Say we wanted to name or variable number of times. Our name is multiple words, but we can't use spaces, so how are we supposed to name it? Kotlin uses camel casing which is a way of naming multi-word names. The first word begins with a lowercase letter, and every subsequent word begins with an uppercase letter. For example, number of times would be numberOfTimes.