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