Kotlin
Putting it together
Build a working CLI app with a menu loop.
Putting it together: a full CLI scenario
All pieces are now ready: the Task data class, TodoList with addTask, listTasks and completeTask. In this final lesson you will combine them into a single scenario.
val list = TodoList()
list.addTask("Shopping")
list.addTask("Homework")
list.addTask("Sport")
list.completeTask("Homework")
list.listTasks()
In a real CLI these calls would happen inside a menu loop driven by user commands. Here we keep the scenario fixed so the output is deterministic.
The menu loop concept
In a real CLI a while (true) loop reads a command from the user and a when dispatches to the right method. In this lesson the scenario is fixed, so there is no loop; but the logic is the same.
while (true) {
val cmd = readln()
when (cmd.substringBefore(':')) {
"add" -> list.addTask(cmd.substringAfter(':'))
"done" -> list.completeTask(cmd.substringAfter(':'))
"list" -> list.listTasks()
else -> return
}
}
This structure lets the user decide the order of commands. In our scenario the order is fixed in the code; this gives a deterministic test output.
Exercise Run the full CLI scenario
In main create a TodoList. Add three tasks in order: list.addTask("Shopping"), list.addTask("Homework"), list.addTask("Sport"). Then complete "Homework" with list.completeTask("Homework") and print all tasks with list.listTasks().
Show example solution
fun main() {
val list = TodoList()
list.addTask("Shopping")
list.addTask("Homework")
list.addTask("Sport")
list.completeTask("Homework")
list.listTasks()
}
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)) }
fun listTasks() { tasks.forEach { println(it.format()) } }
fun completeTask(title: String) {
val i = tasks.indexOfFirst { it.title == title }
if (i >= 0) { tasks[i] = tasks[i].copy(done = true) }
}
}
Test yourself
-
Which sequence adds, completes and lists?
- completeTask, addTask
- addTask, listTasks
- addTask, addTask, addTask, completeTask, listTasks
- listTasks, listTasks, listTasks
Show answer
addTask, addTask, addTask, completeTask, listTasks — Three adds, one complete and one list give the full scenario.
-
Match method to role
- addTask
- Add a task
- completeTask
- Complete a task
- listTasks
- Print all tasks
- copy(done = true)
- New copy, done true
-
Fill in the blank: menu loop
for (cmd ____ menu) list.handle(cmd)
Show answer
for (cmd in menu) list.handle(cmd)
Next lesson: Regex
