Kotlin
Adding tasks
Learn to add tasks with the addTask function.
Adding tasks: TodoList and addTask
Now we will set up a second class to store tasks: TodoList. This class keeps Task objects in a MutableList<Task> and adds new tasks with the addTask method.
class TodoList {
val tasks = mutableListOf<Task>()
fun addTask(title: String) {
tasks.add(Task(title))
}
}
addTask creates a new Task and adds it to the list. The caller only provides the title; object creation stays hidden inside the method.
TodoList and Task together
The TodoList class stores Task objects in a list. addTask adds one element per call. To print the list you can use tasks.forEach { println(it.format()) }.
val list = TodoList()
list.addTask("Shopping")
list.addTask("Homework")
list.tasks.forEach { println(it.format()) }
// [ ] Shopping
// [ ] Homework
In the next step we will move this print into a listTasks method; that way the main code stays simple.
Exercise Define TodoList and addTask
Define a class TodoList with val tasks = mutableListOf<Task>() and fun addTask(title: String) { tasks.add(Task(title)) }. In main create a TodoList, add two tasks, and print them with list.tasks.forEach { println(it.format()) }.
Show example solution
fun main() {
val list = TodoList()
list.addTask("Shopping")
list.addTask("Homework")
list.tasks.forEach { println(it.format()) }
}
data class Task(val title: String, val done: Boolean = false) {
fun format() = if (done) "[x] $title" else "[ ] $title"
}
class TodoList {
val tasks = mutableListOf<Task>()
fun addTask(title: String) {
tasks.add(Task(title))
}
}
Test yourself
-
Fill in the blank: add a Task to the list
tasks.____(Task(title))
Show answer
tasks.add(Task(title))
-
Match expression to role
- MutableList<Task>
- Task list
- addTask(title)
- Adds a new task
- tasks.add(...)
- Appends to the list
- Task(title)
- New task object
-
What should the return type of addTask be?
- Int (index)
- Boolean
- Task (the added one)
- Unit (only appends)
Show answer
Unit (only appends) — addTask returns nothing; it only appends. So it is Unit.
Next lesson: Listing tasks
