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String

Basic String Declaration​

  • Use quotes to create String
  • Use triple quotes """ to create raw String without escaping:
val greeting: String = "Hello, Kotlin!"  
val name = "Jeff" // Type can be inferred
val multiline = """  
    This is a  
    multiline string  
"""

Common String Methods in Kotlin​

  1. length

Returns the number of characters in the string.

val str = "Kotlin"  
println(str.length) // Output: 6
  1. get(index) or str[index]

Returns the character at the specified index (0-based).

Throws IndexOutOfBoundsException if index is invalid.

val ch = "Kotlin"[2]  
println(ch) // Output: t
  1. substring(startIndex, endIndex)

Returns a substring from startIndex up to (but excluding) endIndex.

Throws IndexOutOfBoundsException if indices are invalid.

val sub = "Kotlin".substring(1, 4)  
println(sub) // Output: otl
  1. contains(other: CharSequence, ignoreCase: Boolean = false)

Returns true if the string contains the specified sequence of characters.

ignoreCase lets you ignore case differences.

println("Kotlin".contains("tol"))           // true  
println("Kotlin".contains("TOL", true))    // true (ignore case)  
println("Kotlin".contains("abc"))           // false
  1. startsWith(prefix: String, ignoreCase: Boolean = false)

Returns true if the string starts with the given prefix.

println("Kotlin".startsWith("Kot"))         // true  
println("Kotlin".startsWith("kot", true))  // true (ignore case)
  1. endsWith(suffix: String, ignoreCase: Boolean = false)

Returns true if the string ends with the given suffix.

println("Kotlin".endsWith("lin"))           // true  
println("Kotlin".endsWith("LIN", true))    // true (ignore case)
  1. replace(oldValue: String, newValue: String, ignoreCase: Boolean = false)

Returns a new string with all occurrences of oldValue replaced by newValue.

val replaced = "Kotlin is fun".replace("fun", "awesome")  
println(replaced) // Output: Kotlin is awesome
  1. toUpperCase() and toLowerCase()

Converts the string to uppercase or lowercase letters.

println("Kotlin".toUpperCase()) // Output: KOTLIN  
println("KOTLIN".toLowerCase()) // Output: kotlin
  1. trim()

Removes whitespace characters from the start and end of the string.

val padded = "  Kotlin  "  
println(padded.trim()) // Output: Kotlin
  1. split(delimiter: String, ignoreCase: Boolean = false, limit: Int = 0)

Splits the string into a list of substrings based on the delimiter.

ignoreCase specifies case sensitivity; limit controls the number of splits.

val parts = "a,b,c".split(",")  
println(parts) // Output: [a, b, c]
  1. indexOf(substring: String, startIndex: Int = 0, ignoreCase: Boolean = false)

Returns the index of the first occurrence of substring, or -1 if not found.

println("Kotlin".indexOf("t")) // Output: 2  
println("Kotlin".indexOf("T", ignoreCase = true)) // Output: 2
  1. lastIndexOf(substring: String, startIndex: Int = lastIndex, ignoreCase: Boolean = false)

Returns the index of the last occurrence of substring, or -1 if not found.

println("Kotlin kotlin".lastIndexOf("kotlin", ignoreCase = true)) // Output: 7

String Templates​

Kotlin supports embedding variables or expressions inside strings using $ sign.

  • Use the $ sign followed by a variable name to insert its value into a string.
  • Use ${} to insert an expression or when more complex evaluation is needed.
val name = "Kotlin"  
val age = 14  
println("Hello, $name!")              // Output: Hello, Kotlin!  
println("$name is $age years old.")  // Output: Kotlin is 10 years old.  
println("Next year, $name will be ${age + 1} years old.")  
// Output: Next year, Kotlin will be 15 years old.

You can put any valid Kotlin expression inside ${}.

val items = listOf("apple", "banana", "cherry")  
println("The list has ${items.size} items.") // Output: The list has 3 items.  
println("First item uppercase: ${items[0].uppercase()}")  
// Output: First item uppercase: APPLE

To use a literal $ in a string, escape it with a backslash: \$.

println("Price is \$10")  // Output: Price is $10