List in Java

Java List Interface Explained with Complex Example

In Java, the List interface is a part of the java.util package and represents an ordered collection of elements, allowing duplicates. It extends the Collection interface and provides additional methods to manipulate elements based on their index. The List interface is implemented by several classes in Java, including ArrayList, LinkedList, and others.

List Interface Overview

The List interface is generic, meaning it can work with any data type specified within angular brackets (<>). Here's the basic syntax of the List interface:

public interface List<E> extends Collection<E> {
    // List-specific methods
}

Some of the essential methods provided by the List interface include:

boolean add(E element): Appends the specified element to the end of the list.
void add(int index, E element): Inserts the specified element at the specified position in the list.
E get(int index): Returns the element at the specified position in the list.
int size(): Returns the number of elements in the list.
boolean isEmpty(): Returns true if the list is empty, false otherwise.
E remove(int index): Removes the element at the specified position in the list.
boolean remove(Object obj): Removes the first occurrence of the specified element from the list.
Complex Example: To-Do List Application

Let's illustrate the use of the List interface with a complex example of a simple To-Do List application. In this application, we will create a list of tasks that users can add, remove, and mark as completed. We will use the ArrayList class to implement the List interface.

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

public class ToDoListApp {
    public static void main(String[] args) {
        List<String> toDoList = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);
        int choice;

        do {
            displayMenu();
            choice = scanner.nextInt();
            scanner.nextLine(); // Consume the newline character after reading the integer

            switch (choice) {
                case 1:
                    System.out.print("Enter the task to add: ");
                    String task = scanner.nextLine();
                    toDoList.add(task);
                    System.out.println("Task added: " + task);
                    break;

                case 2:
                    if (!toDoList.isEmpty()) {
                        System.out.println("Current Tasks:");
                        for (int i = 0; i < toDoList.size(); i++) {
                            System.out.println((i + 1) + ". " + toDoList.get(i));
                        }
                        System.out.print("Enter the task number to mark as completed: ");
                        int taskNumber = scanner.nextInt();
                        scanner.nextLine(); // Consume the newline character after reading the integer

                        if (taskNumber >= 1 && taskNumber <= toDoList.size()) {
                            String completedTask = toDoList.remove(taskNumber - 1);
                            System.out.println("Task completed: " + completedTask);
                        } else {
                            System.out.println("Invalid task number.");
                        }
                    } else {
                        System.out.println("No tasks to mark as completed. The list is empty.");
                    }
                    break;

                case 3:
                    if (!toDoList.isEmpty()) {
                        System.out.println("Current Tasks:");
                        for (String task : toDoList) {
                            System.out.println("- " + task);
                        }
                    } else {
                        System.out.println("No tasks to display. The list is empty.");
                    }
                    break;

                case 0:
                    System.out.println("Exiting the To-Do List application.");
                    break;

                default:
                    System.out.println("Invalid choice. Please try again.");
            }

        } while (choice != 0);

        scanner.close();
    }

    private static void displayMenu() {
        System.out.println("\n--- To-Do List ---");
        System.out.println("1. Add Task");
        System.out.println("2. Mark Task as Completed");
        System.out.println("3. View Tasks");
        System.out.println("0. Exit");
        System.out.print("Enter your choice: ");
    }
}

In this example, we use an ArrayList to store the tasks added by the user. The application presents a simple text-based menu to add tasks, mark tasks as completed, view current tasks, and exit the application.

Remember that this example is kept simple for illustration purposes and does not cover error handling or data persistence.

Conclusion

In this blog post, we explored the List interface in Java, which allows us to manage ordered collections of elements. We learned about its basic usage and common methods. To demonstrate its practical application, we developed a To-Do List application using the ArrayList class to implement the List interface. By understanding the List interface, you can effectively work with collections of elements in Java and build more complex applications that require data management and manipulation.

Remember, Java offers various collection interfaces and classes, and the choice of which one to use depends on your specific use case and requirements. Happy coding!