KotlinStrings

Kotlin Strings

Strings are used for storing text.

A string contains a collection of characters surrounded by double quotes:

var greeting = "Hello"

UnlikeJava, you do not have to specify that the variable should be aString. Kotlin is smart enough to understand that the greeting variable in the example above is aString because of the double quotes.

However, just like with other data types, you can specify the type if you insist:

var greeting: String = "Hello"

Note: If you want to create aString without assigning the value (and assign the value later), you must specify the type while declaring the variable:

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

var namename = "John"println(name)

Access a String

To access the characters (elements) of a string, you must refer to theindex number insidesquare brackets.

String indexes start with 0. In the example below, we access the first and third element intxt:

var txt = "Hello World"println(txt[0]) // first element (H)println(txt[2]) // third element (l)

String Length

A String in Kotlin is an object, which contain properties and functions that can perform certain operations on strings, by writing a dot character (.) after the specific string variable. For example, the length of a string can be found with thelength property:

var txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"println("The length of the txt string is: " + txt.length)

String Functions

There are many string functions available, for exampleuppercase() andlowercase():

var txt = "Hello World"println(txt.uppercase())   // Outputs "HELLO WORLD"println(txt.lowercase())   // Outputs "hello world"

Comparing Strings

ThecompareTo(string) function compares two strings and returns 0 if both are equal:

var txt1 = "Hello World"
var txt2 = "Hello World"println(txt1.compareTo(txt2))  // Outputs 0 (they are equal)

Finding a String in a String

TheindexOf() function returns theindex (the position) of the first occurrence of a specified text in a string (including whitespace):

var txt = "Please locate where 'locate' occurs!"println(txt.indexOf("locate"))  // Outputs 7

Quotes Inside a String

To use quotes inside a string, use single quotes ('):

var txt1 = "It's alright"var txt2 = "That's great"

String Concatenation

The+ operator can be used between strings to add them together to make a new string. This is calledconcatenation:

var firstName = "John"var lastName = "Doe"println(firstName + " " + lastName)

You can also use theplus() function to concatenate two strings:

var firstName = "John "var lastName = "Doe"println(firstName.plus(lastName))

String Templates/Interpolation

Instead of concatenation, you can also use "string templates", which is an easy way to add variables and expressions inside a string.

Just refer to the variable with the$ symbol:

var firstName = "John"var lastName = "Doe"println("My name is $firstName $lastName")