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Creating strings

Learn to create strings and use the length property.

Creating strings

A String holds text and is written in double quotes. For example val s = "Hello" creates a String. In Kotlin, Strings are immutable: once created, their content does not change.

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

The length of a String is given by the length property. Unlike Java, there are no parentheses; length is a property, not a method. The first character has index 0, the last has index length - 1. Going beyond throws IndexOutOfBoundsException.

length is a property

In Kotlin, length is a property, not a method. So no parentheses are used: s.length is correct, s.length() is wrong.

val s = "Hello"
val n = s.length   // 5
// s.length()  // compile error

In Java, length() is a method and needs parentheses. When moving to Kotlin this is a common mix-up; the compiler warns you at build time.

For the empty String "", length returns 0.

Practice Create a string and print its length

Write a fun main(). Assign "Alex" to val name. Print the string with println(name) and its length with println(name.length) on separate lines.

Starter code

Main.kt
fun main() {
    // Print the string and its length
}

Sample solution

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

Expected output

Alex
4

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
  • 6 Correct answer
  • 7
  • 0

Explanation: "Kotlin" has 6 characters, length returns 6.

2 Complete the length call

Question 
val n = name.____
Answer 
val n = name.length

Explanation: name.length gives the length (no parens).

3 Match the string concepts

Term Meaning
length Length
"Hello" String example
0 First index
length - 1 Last index

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