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substring

Learn to take parts of a string with substring.

substring

To take a part of a String, use substring(startIndex, endIndex). startIndex is inclusive, endIndex is exclusive.

val s = "Kotlin"
println(s.substring(0, 3))  // Kot
println(s.substring(2, 5))  // tli

Indices start at 0. substring(0, 3) takes characters at 0, 1 and 2; that is the first three letters. The String's length is a safe endIndex.

A single-argument substring(startIndex) also exists; it takes from that index to the end.

Practice Take the first and last three letters

Write a fun main(). Assign "Kotlin" to val lang. Print lang.substring(0, 3) for the first three letters and lang.substring(3, 6) for the last three on separate lines.

Starter code

Main.kt
fun main() {
    // Take the first and last three letters
}

Sample solution

Main.kt
fun main() {
    val lang = "Kotlin"
    println(lang.substring(0, 3))
    println(lang.substring(3, 6))
}

Expected output

Kot
lin

substring with one argument

substring(startIndex) takes one argument and returns the part from that index to the end of the String.

val s = "Kotlin"
println(s.substring(3))  // lin

From index 3 to the end: lin. This is the same as substring(3, s.length) but shorter.

In the two-argument form, endIndex cannot be smaller than startIndex; otherwise IndexOutOfBoundsException is thrown.

Questions and answers

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

1 Complete the substring call

Question 
val part = s.____(0, 3)
Answer 
val part = s.substring(0, 3)

Explanation: s.substring(0, 3) takes the first three characters.

2 What does "Kotlin".substring(2, 5) return?

  • tli Correct answer
  • Kot
  • tlin
  • in

Explanation: Indices 2, 3, 4 give tli.

3 Match the substring results

Term Meaning
substring(0, 3) of "Kotlin" Kot
substring(3) of "Kotlin" lin
substring(2, 5) of "Kotlin" tli
substring(0, 6) of "Kotlin" Kotlin

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