What is a design pattern in programming?

Design pattern in programming is a general solution to typical problems that arise during software development. It is an architectural approach that provides a standardized way to solve specific problems or tasks in programming.

Design patterns help developers create software that is flexible, easily extensible, and easy to maintain. They address specific problems without the need to create new solutions from scratch. Using design patterns helps facilitate understanding and maintenance of code, promotes the use of best practices (best practice), and improves the team's ability to collaborate.

Design patterns can be classified into three main categories.

Simplify the process of creating objects. This category includes, for example, Singleton, Factory Method, Abstract Factory.

Simplify the organization of program structures and interactions between components. These include, for example, Adapter, Composite, Proxy.

Describe ways to organize interactions between objects. These include, for example, Observer, Strategy, Command.

The application of design patterns contributes to the expansion and maintenance of code, as well as facilitates communication among team members of developers. When a developer encounters a typical problem, they can apply the appropriate design pattern, making their code more structured and maintainable. There are many design patterns that are suitable for solving various tasks. A good practice is to analyze the task or problem and determine which pattern fits best in this particular case. It is also important to remember best practices. Below, we will look at the most popular patterns and their areas of application. For a deeper understanding, each pattern should be studied separately. This note provides only a very brief overview (a few sentences).

Defines an interface for creating objects but leaves the choice to subclasses regarding which class to instantiate.

A classic example is the creation of graphical elements (buttons, input fields) in graphical interfaces.

Provides an interface for creating families of related or dependent objects without specifying their concrete classes.

An example is creating graphical elements (buttons, input fields, windows) with a specific style or theme.

Separates the construction process of a complex object from its representation, allowing the same construction process to create different representations.

An example is creating objects with complex configurations, such as a car object with various options.

Allows creating new objects by copying existing objects, providing flexibility and speed in object creation.

An example is creating copies of documents, graphical objects, etc.

Ensures that a class has only one instance and provides a global point of access to it.

An example is a class used to store global settings.

Allows an interface to work with another incompatible interface.

An example is adapting interfaces of different libraries or classes for convenient interaction.

Separates abstraction from implementation, allowing them to vary independently.

An example is separating a graphical interface from its implementation to be able to change both parts independently.

Combines a group of objects into a tree structure to work with them as if they were a single object.

An example is building a tree hierarchy of a file system.

Allows dynamically adding new functionality to objects.

An example is extending the functionality of an object, for instance, adding decorators to graphical objects.

Provides a simple and unified interface to a large group of interfaces in a subsystem.

An example is creating a facade for complex libraries or subsystems for convenient use.

Allows objects to share common parts to save memory.

An example is creating lightweight objects for efficient resource usage.

Allows using special substitute objects instead of real ones. These objects intercept calls addressed to the original object, allowing custom code to be inserted before or after passing the call to the original object.

An example is using a proxy object to control access to a heavy object, such as a large image.

Allows passing requests to handler objects, forming a chain.

An example is processing requests at different levels of a system until the request is handled.

Encapsulates a request as an object, allowing parameterization of clients with requests, objects, and queues.

An example is implementing a request queue.

Provides a way to sequentially access objects without exposing their internal structure.

An example is iterating over elements of a list or collection without revealing their internal structure.

Defines an object that encapsulates how a set of objects interact.

An example is creating a mediator to manage the interaction of a large number of components in a graphical interface.

Provides the ability to store and restore the previous state of an object.

An example is saving the state of a game so that a player can return to previous points.

Defines a dependency between one or more objects and the state of another object.

An example is implementing subscriptions for updates in graphical interfaces or notification systems.

Allows an object to change its behavior when its state changes.

An example is implementing a state machine to control an object's behavior based on conditions. For example, the behavior of NPC depending on its state and environment.

Defines a family of algorithms and makes them interchangeable.

An example is choosing a sorting algorithm depending on the needs of a specific case.

Defines the overall structure of an algorithm, allowing subclasses to modify some steps of the algorithm.

An example is implementing a template for creating similar algorithms.

Allows defining a new operation without changing the classes of objects where it is used.

An example is implementing a visitor to process different types of objects in a complex system.

Creational patterns: