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List operations

Learn list management with add, remove and contains.

List operations: add, remove, contains

On a mutable list the three most common methods are: add(x) appends an element, remove(x) takes out the first match, contains(x) returns a Boolean telling whether x is in the list.

val tasks = mutableListOf("Shopping", "Homework")
tasks.add("Sport")
tasks.remove("Homework")
tasks.contains("Sport")  // true

add always returns true; remove returns true if the element was found and removed, false if it was absent. So you can tell whether the operation succeeded.

Return values of contains and remove

contains(x) returns a Boolean: true if the element is in the list, false otherwise. That is why it fits easily in conditions like if (tasks.contains("Sport")).

val found = tasks.contains("Sport")
val removed = tasks.remove("Missing")
// found: true or false
// removed: false (element was absent)

The Boolean return of remove is handy when you want to remove conditionally: do one thing if it succeeded, try another path if not.

Practice Add, remove and print size

Start with mutableListOf("Ava", "Liam", "Nora"). Add "Maya" to the list, remove "Liam" and print the size with println(names.size).

Starter code

Main.kt
fun main() {
    val names = mutableListOf("Ava", "Liam", "Nora")
    // Add "Maya", remove "Liam" and print size
}

Sample solution

Main.kt
fun main() {
    val names = mutableListOf("Ava", "Liam", "Nora")
    names.add("Maya")
    names.remove("Liam")
    println(names.size)
}

Expected output

3

Questions and answers

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

1 Fill in the blank: append to the list

Question 
tasks.____("Shopping")
Answer 
tasks.add("Shopping")

Explanation: tasks.add("...") appends a new task.

2 What does nums.contains(5) return?

  • Int (index)
  • Unit
  • Boolean (true or false) Correct answer
  • List<Int>

Explanation: contains returns a Boolean; true if present, false if not.

3 Match method to return value

Term Meaning
add(x) true (always)
remove(x) true if removed
contains(x) true if present
size Int

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