ToDoList.java

import java.util.ArrayList;
import java.util.Scanner;

class Task {
    private String description;
    private boolean isCompleted;

    public Task(String description) {
        this.description = description;
        this.isCompleted = false;
    }

    public String getDescription() {
        return description;
    }

    public boolean isCompleted() {
        return isCompleted;
    }

    public void markAsCompleted() {
        this.isCompleted = true;
    }

    @Override
    public String toString() {
        return (isCompleted ? "[X] " : "[ ] ") + description;
    }
}

public class ToDoList {
    private ArrayList<Task> tasks;

    public ToDoList() {
        tasks = new ArrayList<>();
    }

    public void addTask(String description) {
        tasks.add(new Task(description));
    }

    public void deleteTask(int index) {
        if (index >= 0 && index < tasks.size()) {
            tasks.remove(index);
        } else {
            System.out.println("Invalid task number");
        }
    }

    public void markTaskAsCompleted(int index) {
        if (index >= 0 && index < tasks.size()) {
            tasks.get(index).markAsCompleted();
        } else {
            System.out.println("Invalid task number");
        }
    }

    public void displayTasks() {
        if (tasks.isEmpty()) {
            System.out.println("No tasks in the list.");
        } else {
            for (int i = 0; i < tasks.size(); i++) {
                System.out.println((i + 1) + ". " + tasks.get(i));
            }
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        ToDoList toDoList = new ToDoList();
        boolean exit = false;

        while (!exit) {
            System.out.println("\nTo-Do List:");
            toDoList.displayTasks();
            System.out.println("\nOptions:");
            System.out.println("1. Add Task");
            System.out.println("2. Delete Task");
            System.out.println("3. Mark Task as Completed");
            System.out.println("4. Exit");
            System.out.print("Choose an option: ");

            int choice = scanner.nextInt();
            scanner.nextLine();  // Consume the newline

            switch (choice) {
                case 1:
                    System.out.print("Enter task description: ");
                    String description = scanner.nextLine();
                    toDoList.addTask(description);
                    break;
                case 2:
                    System.out.print("Enter task number to delete: ");
                    int deleteIndex = scanner.nextInt() - 1;
                    toDoList.deleteTask(deleteIndex);
                    break;
                case 3:
                    System.out.print("Enter task number to mark as completed: ");
                    int completeIndex = scanner.nextInt() - 1;
                    toDoList.markTaskAsCompleted(completeIndex);
                    break;
                case 4:
                    exit = true;
                    break;
                default:
                    System.out.println("Invalid choice. Please try again.");
            }
        }

        scanner.close();
        System.out.println("To-Do List application closed.");
    }
}