Variables ​

For variables, the declaration might be different Java and Kotlin. This is only cover for Kotlin but will update after I learn it with different language in different section. You can use Kotlin Playground to explore how to write code with Kotlin.

Getting Started ​

Do you familiar with this? Yes, when you start learn programming language, you might start with Hello, World! or Hello World.

fun main() {
    println("Hello, world!")
}

fun main() {
    println("Hello, world!")
}

• fun: represents a function
• main: it's the function name, usually used run the main application (same implementation in Go as well)
• println: it's used to print the information you want to log, it ends with add the new line.
  • print: you can also use print to show the log but it doesn't add new line, so the log will be on the same line if you also put the log after.

Variables ​

For variable declaration, we can use val or var. What's the difference?

• val: used for variable that the value will be static (cannot be changed) or constant.
• var: used for variable that can be modified/changed.

fun main() {
    val name: String = "John"
    println(name)
    
    name = "Doe" // Error: Val cannot be reassigned
    println(name)
}

fun main() {
    val name: String = "John"
    println(name)
    
    name = "Doe" // Error: Val cannot be reassigned
    println(name)
}

fun main() {
    var name: String = "John"
    println(name)
    
    name = "Doe" // Error: Val cannot be reassigned
    println(name)
}

// The output is:
// John
// Doe

fun main() {
    var name: String = "John"
    println(name)
    
    name = "Doe" // Error: Val cannot be reassigned
    println(name)
}

// The output is:
// John
// Doe

There are different ways to declare the variable.

val name: String = "John" // explicitly declare the data type
val age = 17 // kotlin will assign the data type based on value you putts

val name: String = "John" // explicitly declare the data type
val age = 17 // kotlin will assign the data type based on value you putts

Comments ​

The implementation for comments relatively same with other programming languages.

Single-Line Comments ​

To implement it, you can use with two forward slashes (//). You put it above or after the variable, function, etc. You can also use multiple single line comments if you want (or you can use multi-line comments)

For example,

fun main() {
    // This is variable for name
    var name: String = "John"

    println(name) // This is used to print the text
}

fun main() {
    // This is variable for name
    var name: String = "John"

    println(name) // This is used to print the text
}

Multi-Line Comments ​

To implement multi-line, you might need the specific space for the comments. You can start and close with forward slashes and asterisk (/* */) (order matters, open it with /* and close it with */)

For example,

fun main() {
    /*
    * This is variable for name
    */ 
    var name: String = "John"

    println(name)
}

fun main() {
    /*
    * This is variable for name
    */ 
    var name: String = "John"

    println(name)
}

Data Types ​

There are a lot data types in Kotlin (might not complete here).

Data types are divided into different groups:

• Number
• Boolean
• Character
• String

Number Types ​

Number itself divided into 2 (two) groups, Integer and Floating Point.

• Integer: has 4 (four) different types (Byte, Short, Int, and Long), if you're not defined the types, might fallback to Int
• Floating Point: has 2 (two) different types (Float and Double), if you're not defined the types, might fallback to Double

Boolean Type ​

The Boolean data types are true and false

Character Type ​

The Char type can only store a single character and must surrounded by single quotes. It could only take value A-Z and a-z.

For example

fun main() {
    var char: Char = 'J'

    println(char)
}

fun main() {
    var char: Char = 'J'

    println(char)
}

String Type ​

The String type can store sequence of characters like example in the beginning of the page

fun main() {
    val hello: String = "Hello World!"
    println(hello)
}

fun main() {
    val hello: String = "Hello World!"
    println(hello)
}