Introduction to Design Patterns
Creating efficient, reusable code is a key goal for all developers, especially when working on large-scale applications.
A well-organized code structure is essential to avoid duplication when performing similar tasks.
However, extending and adding new features to an existing system can be quite challenging, as developers must fully
understand the system’s intricacies—such as the relationships between entities and the hierarchy they follow.
Additionally, code should be designed to accommodate future changes with minimal effort.
In these situations, having a structured approach to addressing common challenges becomes invaluable.
This is where design patterns come into play.
Design patterns are standard solutions to common software design problems that developers encounter.
They represent best practices and reusable approaches that help in solving recurring design issues in software architecture.
Design patterns are not actual code implementations but templates or guidelines on how to structure code to achieve particular design goals.
Classification of Design Patterns
1. Creational Design Patterns
Creational patterns deal with object creation mechanisms. They abstract the instantiation process to make the system independent of how objects are created.
- Factory Method: Defines an interface for creating objects, but lets subclasses alter the type of objects they create.
- Abstract Factory: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
- Constructor:This is a class-based design pattern that utilizes constructors in a class to create specific types of objects.
- Singleton: Ensures a class has only one instance and provides a global point of access to it.
- Builder: Separates the construction of a complex object from its representation.
- Prototype: Creates new objects by copying an existing object, allowing for easy cloning.
2. Structural Design Patterns
Structural patterns deal with object composition, helping structure classes and objects to form larger systems. They focus on the relationship between entities.
- Adapter: Converts the interface of a class into another interface that clients expect, enabling incompatible interfaces to work together.
- Bridge: Separates an object’s abstraction from its implementation so the two can vary independently.
- Composite: Composes objects into tree structures to represent part-whole hierarchies.
- Decorator: Adds responsibilities to an object dynamically, without modifying its structure.
- Facade: Provides a unified interface to a set of interfaces in a subsystem, simplifying interactions.
- Flyweight: Reduces the cost of creating large numbers of similar objects by sharing common state.
- Proxy: Provides a surrogate or placeholder for another object to control access to it.
3. Behavioral Design Patterns
Behavioral patterns focus on communication between objects, managing how objects interact with each other in a system.
- Chain of Responsibility: Passes a request along a chain of handlers, each having the chance to process it or pass it along the chain.
- Command: Encapsulates a request as an object, allowing for parameterization of clients with different requests.
- Interpreter: Defines a grammar and interprets sentences of that grammar within a given context.
- Iterator: Provides a way to sequentially access the elements of a collection without exposing its underlying representation.
- Mediator: Reduces communication complexity by centralizing communication between classes in a mediator object.
- Memento: Captures an object’s internal state to be restored later without violating encapsulation.
- Observer: Defines a dependency between objects so that when one changes state, others are notified and updated automatically.
- State: Allows an object to change its behavior when its internal state changes.
- Strategy: Defines a family of algorithms, encapsulates each one, and makes them interchangeable.
- Template Method: Defines the skeleton of an algorithm, with steps deferred to subclasses.
- Visitor: Allows adding new operations to a class hierarchy without modifying the existing classes.
4. Architectural Design Patterns
Architectural patterns deal with the high-level structure of the entire system, ensuring scalability, maintainability, and robustness.
- Layered Architecture: Organizes the system into layers, with each layer having a specific responsibility.
- Microservices Architecture: Structures the system as a collection of loosely coupled, independently deployable services.
- Event-Driven Architecture: Encourages the production, detection, and consumption of events to drive application behavior.
- Client-Server Architecture: Defines a relationship between clients (requesters of services) and servers (providers of services).
- Model-View-Controller (MVC): Separates an application into three main components: Model, View, and Controller.