Kotlin Strings

Kotlin Strings – Your Text Toolbox

In Kotlin, strings are like little boxes full of characters wrapped in double quotes.

var message = "Hey there!"

Kotlin's smart brain detects it's a string just by the quotes. No need to shout out "String"—unless you want to.

Want to be explicit?

If you feel fancy, you can mention the type directly:

var welcome: String = "Hi!"

Declare now, assign later?

Sure! But only if you label the type from the start:

This is fine:

var name: String 
Name = "Alice" 

This throws an error:

var name
Name = "Alice" // Error: Kotlin doesn't know what type this is 

Accessing Letters in a String

Each letter in a string has a position number (starting from 0). Use square brackets to pick a letter:

val txt = "Kotlin" 
println(txt[0]) // K 
Println(txt[2]) // t 

Positions go like this:

0 = first, 1 = second, 2 = third… you get the idea.

String Size – Count the Letters

You can measure how long a string is using .length:

val alpha = "ABCDEF" 
Println(alpha.length) // 6 

Kotlin treats strings as objects, so you can call functions and properties on them!

String Power Tools (Functions)

Kotlin strings come with built-in helpers:

val word = "Hello World" 
println(word.toUpperCase()) // HELLO WORLD 
Println(word.toLowerCase()) // hello world 

Great for formatting, search, or clean-up.

Compare Two Strings

Want to check if two strings match? Use .compareTo():

val a = "Hello" 
val b = "Hello" 
Println(a.compareTo(b)) // 0 → same 

Returns 0 when they're equal.

Find Text Inside a String

Use .indexOf() to locate text:

val line = "Find where this word starts" 
Println(line.indexOf("this")) // Outputs 10 

Starts counting from 0, just like everything else in Kotlin.

Using Quotes Inside Quotes

Want ' in a string? No problem:

val one = "It's awesome" 
Val two = "That's amazing" 

Kotlin handles single quotes inside double quotes just fine.

Merging Text – String Join

With Plus Sign:

val first = "Jane" 
val last = "Doe" 
Println(first + " " + last) 

With .plus() method:

println(first.plus(last)) // Same output 

String Templates – Insert Variables Easily

This is Kotlin's superpower! Use $ to plug variables directly:

val user = "Sahand" 
val role = "Developer" 
Println("Hi, I’m $user, a $role") 

You can also add expressions:

val age = 30 
Println("Next year, I’ll be ${age + 1}") 

No messy + symbols. Just clean, readable strings!

Summary Table – String Essentials