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Putting it together

Combine all parts into a working final app.

Putting it together: the full flow

In the final lesson you combine all pieces: adding tasks, completing one and printing the completed ones. The app becomes a small sample of a real task tracker.

val list = TaskList()
list.addTask("Study Kotlin")
list.addTask("Shopping")
list.complete(0)
println(list.listDone())
// [[x] Study Kotlin]

This flow calls addTask, complete and listDone one after another. Each is a piece you defined in previous lessons. This completes a real use case.

Flow design

The app flow is: first add tasks to the list, then complete one, finally print the completed ones. Each step calls a method defined in earlier lessons.

list.addTask("Study Kotlin")    // L02
list.addTask("Shopping")        // L02
list.complete(0)                 // L04
println(list.listDone())         // L03

This flow shows the power of cumulative design. Each lesson added one piece and the final lesson put them together. In the real world, apps grow this way too.

Practice Combine the whole flow

In main create val list = TaskList(). Call list.addTask("Study Kotlin") and list.addTask("Shopping"). Complete the first task with list.complete(0). Finally print list.listDone() with println.

Starter code

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

class TaskNotFound(message: String) : Exception(message)

class TaskList {
    val tasks = mutableListOf<Task>()
    fun addTask(title: String) {
        tasks.add(Task(title))
    }
    fun listDone() = tasks.filter { it.done }
    fun complete(index: Int) {
        if (index >= tasks.size) throw TaskNotFound("Görev yok: $index")
        tasks[index].done = true
    }
}

fun main() {
    val list = TaskList()
    // Add two tasks, complete one, print the done ones
}

Sample solution

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

class TaskNotFound(message: String) : Exception(message)

class TaskList {
    val tasks = mutableListOf<Task>()
    fun addTask(title: String) {
        tasks.add(Task(title))
    }
    fun listDone() = tasks.filter { it.done }
    fun complete(index: Int) {
        if (index >= tasks.size) throw TaskNotFound("Görev yok: $index")
        tasks[index].done = true
    }
}

fun main() {
    val list = TaskList()
    list.addTask("Study Kotlin")
    list.addTask("Shopping")
    list.complete(0)
    println(list.listDone())
}

Expected output

[[x] Kotlin çalış]

Questions and answers

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

1 Match method to purpose

Term Meaning
addTask Add task
complete Finish task
listDone Get done tasks
TaskNotFound Error type

2 How are branches chosen in this project?

  • Only for
  • Only if
  • with when branches Correct answer
  • Only try

Explanation: The project flow uses when branches.

3 Fill in the blank: call complete

Question 
try {
    list.____(0)
} catch (e: TaskNotFound) {
    println(e.message)
}
Answer 
try {
    list.complete(0)
} catch (e: TaskNotFound) {
    println(e.message)
}

Explanation: list.complete(0) completes the first task.

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