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Kotlin String

The String class represents an array of char types. Strings are immutable which means the length and elements cannot be changed after their creation.

Unlike Java, Kotlin does not require a new keyword to instantiate an object of a String class. A String can be simply declared within double quote (" ") known as escaped string or triple quote(""" """) known as raw string.

Kotlin String Property

Property Description
length: Int It returns the length of string sequence.
indices: IntRange It returns the ranges of valid character indices from current char sequence.
lastIndex: Int It returns the index of last character from char sequence.

String Function

Functions Description
compareTo(other: String): Int It compares the current object with specified object for order. It returns zero if current is equals to specified other object.
get(index: Int): Char It returns the character at given index from the current character sequence.
plus(other: Any?): String It returns the concatenate string with the string representation of the given other string.
subSequence(startIndex: Int,endIndex: Int): CharSequence It returns the new character sequence from current character sequence, starting from startIndex to endIndex.
CharSequence.contains(other: CharSequence, ignoreCase: Boolean = false):Boolean It returns true if the character sequence contains the other specified character sequence.
CharSequence.count(): Int It returns the length of char sequence.
String.drop(n: Int): String It returns a string after removing the first n character.
String.dropLast(n: Int): String It returns a string after removing the last n character.
String.dropWhile
(predicate: (Char) -> Boolean
): String
It returns a character sequence which contains all the characters, except first characters which satisfy the given predicate.
CharSequence.elementAt(index: Int): Char It returns a character at the given index or throws an IndexOutOfBoundsException if the index does not exist in character sequence.
CharSequence.indexOf(char: Char, startIndex: Int = 0,
ignoreCase: Boolean = false
): Int
It returns the index of first occurrence of the given character, starting from the given index value.
CharSequence.indexOfFirst(
predicate: (Char) -> Boolean
): Int
It returns the index of first character which match the given predicate, or -1 if the character sequence not contains any such character.
CharSequence.indexOfLast(
predicate: (Char) -> Boolean
): Int
It returns the index of last character which match the given predicate, or -1 if the character sequence not contains any such character.
CharSequence.getOrElse(index: Int, defaultValue: (Int) ->Char): Char It returns the character at specified index or the result of calling the defaultValue function if the index is out of bound of current character sequence.
CharSequence.getOrNull(index: Int): Char? It returns a character at the given index or returns null if the index is out of bound from character sequence.

String elements and templates

String elements

The characters which are present in string are known as elements of string. Element of string are accessed by indexing operation string[index]. String's index value starts from 0 and ends at one less than the size of string string[string.length-1]. Index 0 represent first element, index 1 represent second element and so on.

Example of accessing string element

Output:

H
e
!

String templates

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.

String template as variable name:

Output:

i=10

String template as arbitrary expression in curly braces:

String template is also used in arbitrary expression in curly braces to evaluate a string expression. This is done by using dollar sign $.

abc is a string which length is 3

String template in raw string:

Output:

value 10
is greater than value 5

Kotlin String Literals

Kotlin has two types of string literals:

  • Escaped String
  • Raw String

Escaped String

Escape String is declared within double quote (" ") and may contain escape characters like '\n', '\t', '\b' ,'\r','\$'etc.

Raw String

Row String is declared within triple quote (""" """).It provides facility to declare String in new lines and contain multiple lines. Row String cannot contain any escape character.

While using raw string with new line, it generates a | as margin prefix. For example:

Output:

Kotlin is official language
        |announce by Google for
        |android application development

String trimMargin() function

Leading whitespace can be removed with trimMargin() function. By default, trimMargin() function uses | as margin prefix.

Output:

Kotlin is official language
announce by Google for
android application development

However, it can be change by passing a new string inside trimMargin() function.

Output:

Kotlin is official language
announce by Google for
android application development

Kotlin String Equality

In Kotlin, strings equality comparisons are done on the basis of structural equality (==) and referential equality (===).

In structural equality two objects have separate instances in memory but contain same value.

Referential equality specifies that two different references point the same instance in memory.

Structural equality (==)

To check the two objects containing the same value, we use == operator or != operator for negation. It is equivalent to equals() in java.

Output:

true
false

Referential equality (===)

To check the two different references point to the same instance, we use === operator. The !== operator is used for negation. a === b specifies true if and only if a and b both point to the same object.

Let's see an example of referential equality to check different reference contains same instance or not. For creating string we are using a helper method buildString rather than using quotes.

Output:

false
true





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