What design patterns from well-known ones have you used in your projects?

In my projects, I have used several common design patterns that help make the code more structured and maintainable:

• Singleton — for creating a single instance of a class, for example, for a settings manager or database connection.

• Factory Method — for creating objects without specifying the exact class, which facilitates extending functionality.

• Observer — for implementing subscription and notification mechanisms, for example, in UI when data changes.

• Decorator — for dynamically adding functionality to objects without changing their structure.

• MVC/MVP/MVVM — architectural patterns that separate logic, presentation, and data, especially in Android development.

Example of a simple Singleton in Java:

public class DatabaseConnection {
    private static DatabaseConnection instance;

    private DatabaseConnection() {
        // initialization
    }

    public static synchronized DatabaseConnection getInstance() {
        if (instance == null) {
            instance = new DatabaseConnection();
        }
        return instance;
    }
}

Using patterns helps improve code readability, testability, and scalability.