Classes

Set up the data model with class and constructor.

The TaskList class and mutableListOf

To manage multiple tasks you write a TaskList class. It contains a mutableListOf<Task>() and an addTask method that adds a new task.

class TaskList {
    val tasks = mutableListOf<Task>()
    fun addTask(title: String) {
        tasks.add(Task(title))
    }
}

addTask takes a title, creates a new Task and adds it to the list. mutableListOf gives a mutable list; add appends a new element. This makes adding a task a one-liner.

Print the list

println(list.tasks) prints the whole list. The list's toString separates items with commas and wraps them in square brackets. Each Task's own toString is called.

list.addTask("Study Kotlin")
list.addTask("Shopping")
println(list.tasks)
// [[ ] Study Kotlin, [ ] Shopping]

This lets you see the list contents without writing a separate loop. Notice how the toString design in the Task class pays off here. A good toString makes debugging easier.

Exercise Add two tasks and print them

Add a fun addTask(title: String) method to the TaskList class: create a new Task and add it to the tasks list. In main call list.addTask("Study Kotlin") and list.addTask("Shopping"), then print list.tasks with println.

Show example solution

class Task(val title: String) {
    var done: Boolean = false
    override fun toString(): String {
        return if (done) "[x] $title" else "[ ] $title"
    }
}

class TaskList {
    val tasks = mutableListOf<Task>()
    fun addTask(title: String) {
        tasks.add(Task(title))
    }
}

fun main() {
    val list = TaskList()
    list.addTask("Study Kotlin")
    list.addTask("Shopping")
    println(list.tasks)
}

Test yourself

Match concept to purpose

mutableListOf<Task>

Task list
addTask(String)

Add task
new Task

Create object
tasks.add

Put in list
What does addTask("Study Kotlin") do?
- Removes a task from the list
- Prints the list
- Completes the task
- Creates a new Task and adds it to the list
Show answer

Creates a new Task and adds it to the list — addTask creates a new Task object and adds it to the list.

Fill in the blank: call addTask

val list = TaskList()
list.____("Study Kotlin")

Show answer

val list = TaskList()
list.addTask("Study Kotlin")

Next lesson: Collections

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies