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Strings in Kotlin

String Equality​

In Kotlin strings are compared with == operator which chect for their structural equality.

val str1 = "Hello, World!"
val str2 = "Hello," + " World!"
println(str1 == str2) // Prints true

Referential equality is checked with === operator.

val str1 = """
    |Hello, World!
    """.trimMargin()

val str2 = """
    #Hello, World!
    """.trimMargin("#")

val str3 = str1

println(str1 == str2) // Prints true
println(str1 === str2) // Prints false
println(str1 === str3) // Prints true

String Literals​

Kotlin has two types of string literals:

  • Escaped string
  • Raw string

Escaped string handles special characters by escaping them. Escaping is done with a backslash. The following escape sequences are supported: \t, \b, \n, \r, \', \", \\ and \$. To encode any other character, use the Unicode escape sequence syntax: \uFF00.

val s = "Hello, world!\n"

Raw string delimited by a triple quote """, contains no escaping and can contain newlines and any other characters

val text = """
    for (c in "foo")
        print(c)
"""

Leading whitespace can be removed with trimMargin() function.

val text = """
    |Tell me and I forget.
    |Teach me and I remember.
    |Involve me and I learn.
    |(Benjamin Franklin)
    """.trimMargin()

Default margin prefix is pipe character |, this can be set as a parameter to trimMargin; e.g. trimMargin(">").

Elements of String​

Elements of String are characters that can be accessed by the indexing operation string[index].

val str = "Hello, World!"
println(str[1]) // Prints e

String elements can be iterated with a for-loop.

for (c in str) {
    println(c)
}

String Templates​

Both escaped strings and raw strings can contain template expressions. Template expression is a piece of code which is evaluated and its result is concatenated into string. It starts with a dollar sign $ and consists of either a variable name:

val i = 10
val s = "i = $i" // evaluates to "i = 10"

Or an arbitrary expression in curly braces:

val s = "abc"
val str = "$s.length is ${s.length}" // evaluates to "abc.length is 3"

To include a literal dollar sign in a string, escape it using a backslash:

val str = "\$foo" // evaluates to "$foo"

The exception is raw strings, which do not support escaping. In raw strings you can use the following syntax to represent a dollar sign.

val price = """
${'$'}9.99
"""