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String

Learn the String type and its methods.

String

A String is a sequence of zero or more characters. It is written between double quotes: "Hello". In Kotlin, strings are immutable; once created, their content does not change.

Common operations: length, uppercase(), substring(b, e).

val s = "Kotlin"
println(s.length)      // 6
println(s.uppercase()) // KOTLIN

Practice String operations

Write a fun main(). Declare val name = "kotlin". Print with println(name.length) and println(name.uppercase()).

Sample solution

Main.kt
fun main() {
    val name = "kotlin"
    println(name.length)
    println(name.uppercase())
}

Expected output

6
KOTLIN

String concatenation

You can concatenate two strings with +: "Hello " + "Kotlin" → "Hello Kotlin". But a more readable approach is a string template: "Hello $name".

Templates are shorter than concatenation and convert the variable's type to a string automatically. Numeric values can also be embedded directly as $n.

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does `"Kotlin".length` return?

  • 5
  • 7
  • It throws an error
  • 6 Correct answer

Explanation: "Kotlin" has 6 characters.

2 String: match the terms

Term Meaning
length Length
uppercase() Uppercase
substring() Substring
lowercase() Lowercase

3 String: fill in the missing part

Question 
val s = "kotlin"
println(s.____())
Answer 
val s = "kotlin"
println(s.uppercase())

Explanation: uppercase() converts the String to uppercase.

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together