Kotlin String

An array of characters is called a string. Kotlin strings are mostly similar to Java strings but has some new added functionalities. Kotlin strings are also immutable in nature means we can not change elements and length of the String. 
The String class in Kotlin is defined as: 

class String : Comparable<String>, CharSequence

To declare a string in Kotlin, we need to use double quotes(” “), single quotes are not allowed to define Strings.
Syntax: 

var variable_name = "Hello, Geeks"   
or
var variable_name : String = "GeeksforGeeks"

Creating an empty String: 
To create an empty string in Kotlin, we need to create an instance of String class. 

var variable_name = String()

String elements and templates –

String Element –
The character, digit or any other symbol present in string is called as element of a String. We can easily access the element of the string using string[index]. Elements store in a string from index 0 to (string.length – 1).
There are three ways in which you can access string elements in Kotlin – 

1. Using index: Returns the character at specified index.
2. Using get function: Returns the character at specified index passed as argument to get function.
3. Iterating over the String: Using loops to access the characters in the String.

Kotlin program to access the elements of a string –

Java

fun main(args: Array<String>){
    // accessing string elements one by one
    var str = "Hello"
    println(str[0])
    println(str[1])
    println(str[2])
    println(str[3])
    println(str[4])
    // accessing the string elements using for loop
    var str2 = "Geeks"
    for(i in str2.indices){
        print(str2[i]+" ")
    }
}

Output:

H
e
l
l
o
G e e k s 

String Template –
String template expression is a piece of code which is evaluated and its result is returned into string. Both string types (escaped and raw string) contain template expressions. String templates starts with a dollar sign $ which consists either a variable name or an arbitrary expression in curly braces. 

Java

fun main(args: Array<String>) {

    var n = 10
    println("The value of n is $n")
    // using string
    val str = "Geeks"
    println("$str is a string which length is ${str.length}")
}

Output:

The value of n is 10
Geeks is a string which length is 5

Some important properties and functions in String:

• Length: Returns the length of the String. 
  

var s =" String"
println(s.length)

• get(index): Returns the character at that particular index. 
  

s.get(3) // Output: - i

• subSequence(start, end):Returns a substring starting from start and ending at end but excluding end. 
  

s.subSequence(1, 4) // Output: - tri

• str.compareTo(string): Returns 0 if str == string. 
  

Kotlin program of using the above properties and functions –

Java

fun main(args: Array<String>) {
    var g = "GeeksForGeeks"
    var e = "Geeks"
    println(g.length)
    println(g.get(4))
    println(g.subSequence(0, 5))
    println(g.compareTo(e))
}

Output:

13
s
Geeks
8

String literals –

There are two types of string literals in Kotlin – 

1. Escaped String
2. Raw String

Escaped String
Escaped string is declared with double quotes (“….”) and it may contain escape characters like /n, /t etc.
Kotlin program of escaped string –

Java

fun main(args: Array<String>) {
    // escaped string
    val str = "World \n is \n amazing"
    println(str)
}

Output:

World 
 is 
 amazing

Raw String – Multi-line String
Raw string is placed inside the triple quotes (“””….”””) and it does not have escape characters. It provides the facility of writing the string into multiple lines so it is also called multi-line string.
Kotlin program of raw string –

Java

fun main(args: Array<String>) {
// raw string - multiline string
    var str = """My
        |name
        |is
        |Yash
    """.trimMargin()
    println(str)
}

Output:

My
name
is
Yash

Escape Characters – Some of the escape characters are: – 

• \” : for double quote
• \r : for carriage return
• \n : for newline
• \’ : for single quote
• \\ : for backslash
• \t : for tab
• \b : for backspace

String Equality –

Kotlin provides an additional feature of comparing the instances of a particular type in two different ways. This feature makes Kotlin different than the other programming languages. 
The two types of equality are – 

• Structural Equality
• Referential Equality

Structural Equality –
Structural equality is checked through the == operator and its inverse != operator. By default, the expression containing x==y is translated into the call of equals() function for that type. 
Referential Equality –
The referential equality in Kotlin is checked through the === operator and its inverse !== operator. This equality returns true only if both the instances of a type point to the same location in memory. When used on types that are converted into primitives type at runtime, the === check is converted into == check and !== check is converted into != check.
Kotlin program to demonstrate the structural and referential equality –

Java

fun main(args: Array<String>) {
    var x = "GeeksForGeeks"
    var y = "GeeksForGeeks"
    var z = "Geeks"
    println(x===y) // true , as both are pointing to the same StringPool
    println(x==z) //false since values are not equal
    println(x===z) //false
}

Output:

true
false
false