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Summary - Lists

Combine mutableListOf, add and map to write a class list.

Summary: build a list, add, transform

In this summary you will combine mutableListOf, add and map to process a class list. First build a mutable list, add a new student, then upper-case every name with map.

val students = mutableListOf("Ava", "Liam")
students.add("Nora")
val big = students.map { it.uppercase() }
// [AVA, LIAM, NORA]

This chain shows both the mutable (add) and the transformable (map) side of lists.

Practice Grow and transform the class list

Start with mutableListOf("Ava", "Liam"), add "Nora" with add, then upper-case every name with map { it.uppercase() } and print the result with println.

Starter code

Main.kt
fun main() {
    // Build a mutable list of two students, add one more,
    // upper-case the names and print
}

Sample solution

Main.kt
fun main() {
    val students = mutableListOf("Ava", "Liam")
    students.add("Nora")
    println(students.map { it.uppercase() })
}

Expected output

[AVA, LIAM, NORA]

Practice Pick the long names with filter

Create a mutableListOf("Ava", "Liam", "Nora"). Use filter { it.length > 3 } to keep names longer than 3 characters and print the result with println.

Starter code

Main.kt
fun main() {
    val students = mutableListOf("Ava", "Liam", "Nora")
    // Filter names longer than 3 characters and print
}

Sample solution

Main.kt
fun main() {
    val students = mutableListOf("Ava", "Liam", "Nora")
    val longNames = students.filter { it.length > 3 }
    println(longNames)
}

Expected output

[Liam, Nora]

Questions and answers

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

1 Which chain works correctly?

  • mutableListOf + add + filter { it.uppercase() }
  • listOf + add + map { it.uppercase() }
  • mutableListOf + put + map { it.uppercase() }
  • mutableListOf + add + map { it.uppercase() } Correct answer

Explanation: mutableListOf accepts add; map produces the upper-case list.

2 Match chain step to role

Term Meaning
mutableListOf Mutable start
add Appends an element
map { } Transforms each element
uppercase() Upper-cases letters

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