Practice Project: Task Manager - Part 2

Let's think about it this way

In Part 1, we got as far as creating the task list and adding tasks. In this part, we'll use Kotlin's collection functions — filter, find, forEach — along with lambda expressions to add search/filter/status-update features to the task list. A higher-order function is a function that can accept another function as a parameter, so the caller can pass in custom filter logic as a lambda. We'll use a when expression to make task status changes more readable, and combine it with the safe call operator for null safety, so a missing task doesn't trigger an error.

Let's build it

Add 3 more functions to the TaskManager class — completeTask(id: Int) finds the task with tasks.find { it.id == id }, sets isDone = true, and shows "Task not found" if no task matches. filterByPriority(priority: Priority) uses a filter lambda to return the task list by priority. Write a higher-order function searchTasks(predicate: (Task) -> Boolean) that lets the caller pass a custom condition (e.g. title contains a keyword) as a lambda. In main(), try completing a task, filtering for just HIGH priority tasks, then call searchTasks with a lambda like title.contains("Kotlin").

• completeTask function can find a task with find and update its status
• filterByPriority function can filter the list with a filter lambda
• The higher-order function searchTasks can be called with a custom lambda predicate

Code Example

class TaskManager {
    private val tasks = mutableListOf<Task>()

    fun addTask(title: String, priority: Priority) {
        if (title.isBlank()) return
        tasks.add(Task(id = tasks.size + 1, title = title, priority = priority))
    }

    fun completeTask(id: Int) {
        val task = tasks.find { it.id == id }
        if (task != null) {
            task.isDone = true
            println("Task #${task.id} completed: ${task.title}")
        } else {
            println("Task not found: #$id")
        }
    }

    fun filterByPriority(priority: Priority): List<Task> =
        tasks.filter { it.priority == priority }

    fun searchTasks(predicate: (Task) -> Boolean): List<Task> =
        tasks.filter(predicate)

    fun printAll() = tasks.forEach { println("#${it.id} - ${it.title} (${it.priority}) done=${it.isDone}") }
}

fun main() {
    val manager = TaskManager()
    manager.addTask("Kotlin syntax ပြန်ကြည့်ရန်", Priority.HIGH)
    manager.addTask("Data class ကျင့်ရန်", Priority.MEDIUM)
    manager.addTask("Lambda ကျင့်ရန်", Priority.HIGH)

    manager.completeTask(1)
    println("--- HIGH priority tasks ---")
    manager.filterByPriority(Priority.HIGH).forEach { println(it.title) }

    println("--- Search 'Kotlin' ---")
    manager.searchTasks { it.title.contains("Kotlin") }.forEach { println(it.title) }
}

You'll see a message confirming Task #1 was completed, along with a list of two HIGH priority tasks and one task containing 'Kotlin'.