Solved Exercises – ArrayList in Java

import java.util.ArrayList;

public class EvenNumberFilter {
    public static void main(String[] args) {
        // 1. Create an ArrayList that can store Integer objects.
        ArrayList numbers = new ArrayList<>();

        // 2. Add the numbers 1, 5, 10, 15, 20, 25 to the ArrayList.
        numbers.add(1);
        numbers.add(5);
        numbers.add(10);
        numbers.add(15);
        numbers.add(20);
        numbers.add(25);

        // 3. Create a new empty ArrayList called evenNumbers.
        ArrayList evenNumbers = new ArrayList<>();

        // 4. Iterate through the first ArrayList. For each number, check if it's even. If it is, add it to the evenNumbers ArrayList.
        for (int number : numbers) {
            if (number % 2 == 0) {
                evenNumbers.add(number);
            }
        }

        // 5. Print both the original ArrayList and the evenNumbers ArrayList.
        System.out.println("Original ArrayList: " + numbers);
        System.out.println("Even Numbers ArrayList: " + evenNumbers);
    }
}

import java.util.ArrayList;
import java.util.List;

public class CombineAndRemoveDuplicates {
    public static void main(String[] args) {
        // 1. Create two ArrayLists of String objects:
        List list1 = new ArrayList<>();
        list1.add("apple");
        list1.add("banana");
        list1.add("orange");
        list1.add("apple");

        List list2 = new ArrayList<>();
        list2.add("banana");
        list2.add("grape");
        list2.add("kiwi");
        list2.add("orange");

        // 2. Create a new ArrayList called combinedList.
        List combinedList = new ArrayList<>();

        // 3. Add all elements from list1 to combinedList.
        combinedList.addAll(list1);

        // 4. Add all elements from list2 to combinedList.
        combinedList.addAll(list2);

        // 5. Create another new ArrayList called uniqueList.
        List uniqueList = new ArrayList<>();

        // 6. Iterate through combinedList. For each element, if it's not already present in uniqueList, add it to uniqueList.
        for (String item : combinedList) {
            if (!uniqueList.contains(item)) {
                uniqueList.add(item);
            }
        }

        // 7. Print combinedList and uniqueList.
        System.out.println("Combined List: " + combinedList);
        System.out.println("Unique List: " + uniqueList);
    }
}

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class SortByLength {
    public static void main(String[] args) {
        // 1. Create an ArrayList of String objects: "short", "longerstring", "medium", "a", "verylongstringindeed".
        List strings = new ArrayList<>();
        strings.add("short");
        strings.add("longerstring");
        strings.add("medium");
        strings.add("a");
        strings.add("verylongstringindeed");

        // 2. Sort the ArrayList based on the length of the strings in ascending order.
        Collections.sort(strings, Comparator.comparingInt(String::length));

        // 3. Print the sorted ArrayList.
        System.out.println("Sorted by Length: " + strings);
    }
}

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

public class TodoList {
    private List tasks;

    public TodoList() {
        this.tasks = new ArrayList<>();
    }

    public void addTask(String task) {
        this.tasks.add(task);
        System.out.println("Task '" + task + "' added.");
    }

    public void viewTasks() {
        if (tasks.isEmpty()) {
            System.out.println("Your to-do list is empty.");
        } else {
            System.out.println("--- To-Do List ---");
            for (int i = 0; i < tasks.size(); i++) {
                System.out.println((i + 1) + ". " + tasks.get(i));
            }
            System.out.println("------------------");
        }
    }

    public void markAsDone(int index) {
        if (index >= 1 && index <= tasks.size()) {
            String removedTask = tasks.remove(index - 1);
            System.out.println("Task '" + removedTask + "' marked as done (removed).");
        } else {
            System.out.println("Invalid task number.");
        }
    }

    public static void main(String[] args) {
        TodoList todoList = new TodoList();
        Scanner scanner = new Scanner(System.in);
        int choice;

        do {
            System.out.println("\n--- To-Do List Menu ---");
            System.out.println("1. Add Task");
            System.out.println("2. View Tasks");
            System.out.println("3. Mark Task as Done");
            System.out.println("4. Exit");
            System.out.print("Enter your choice: ");
            choice = scanner.nextInt();
            scanner.nextLine(); // Consume newline

            switch (choice) {
                case 1:
                    System.out.print("Enter task to add: ");
                    String newTask = scanner.nextLine();
                    todoList.addTask(newTask);
                    break;
                case 2:
                    todoList.viewTasks();
                    break;
                case 3:
                    System.out.print("Enter the number of the task to mark as done: ");
                    int taskNumber = scanner.nextInt();
                    todoList.markAsDone(taskNumber);
                    scanner.nextLine(); // Consume newline
                    break;
                case 4:
                    System.out.println("Exiting to-do list application. Goodbye!");
                    break;
                default:
                    System.out.println("Invalid choice. Please try again.");
            }
        } while (choice != 4);

        scanner.close();
    }
}