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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.

Practice 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().

Starter code

Main.kt
fun main() {
    val list = TodoList()
    // Add 3 tasks, complete one of them, print with listTasks
}

// The Task and TodoList classes stay as defined in the previous lesson.

Sample solution

Main.kt
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) }
    }
}

Expected output

[ ] Shopping
[x] Homework
[ ] Sport

Questions and answers

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

1 Which sequence adds, completes and lists?

  • completeTask, addTask
  • addTask, listTasks
  • addTask, addTask, addTask, completeTask, listTasks Correct answer
  • listTasks, listTasks, listTasks

Explanation: Three adds, one complete and one list give the full scenario.

2 Match method to role

Term Meaning
addTask Add a task
completeTask Complete a task
listTasks Print all tasks
copy(done = true) New copy, done true

3 Fill in the blank: menu loop

Question 
for (cmd ____ menu) list.handle(cmd)
Answer 
for (cmd in menu) list.handle(cmd)

Explanation: for (cmd in menu) walks the command sequence.

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