Quick Guide to Design Patterns at a High Level

What are Design Patterns?

Design patterns are essential tools for developing efficient and reusable code. They are standardised solutions to common problems in software design, facilitating the creation of scalable and maintainable code structures. As applications grow in complexity, design patterns become integral to the style guide, helping developers avoid redundant code and streamline feature additions. By understanding the relationships and hierarchies between different components, developers can make their code adaptable to future changes. This is where design patterns shine, providing pre-defined templates to solve recurring design challenges.

Advantages and Objectives of Design Patterns

Design patterns offer several significant benefits:

Optimized Solutions: Derived and refined by experienced programmers, design patterns provide tried-and-true solutions that enhance code efficiency and correctness.

• Reusability: These patterns act as generic templates that can be customized to address various problems, promoting code reuse.
• Clarity and Elegance: By avoiding repetitive code, design patterns lead to cleaner and more elegant solutions.
• Development Efficiency: With a solid template in place, developers can focus more on the overall quality and functionality of the application rather than the code structure itself.

Classification of Design Patterns

Design patterns are generally classified into four main categories:

1- Creational
2- Structural
3- Behavioural
4- Architectural

Creational Design Patterns

Creational design patterns provide mechanisms for object creation, abstracting the instantiation process. These patterns help in managing object creation complexities and provide flexibility in deciding which objects to create based on the specific situation.

Examples:

• Factory: Creates objects without specifying the exact class of object that will be created.
• Constructor: Ensures a class only has one instance and provides a global point of access to it.
• Singleton: Restricts instantiation of a class to a single object.
• Builder: Allows the construction of complex objects step by step.
• Prototype: Creates new objects by copying an existing object, known as the prototype.
• Abstract Factory: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.

Structural Design Patterns

Structural design patterns deal with object composition and relationships. They help ensure that if one part of a system changes, the entire system doesn’t need to change. These patterns make it easier to add new functionalities to objects without altering their structure.

Examples:

• Decorator: Adds responsibilities to objects dynamically.
• Facade: Provides a simplified interface to a complex subsystem.
• Bridge: Separates an object’s interface from its implementation.
• Adapter: Allows incompatible interfaces to work together.
• Composite: Composes objects into tree structures to represent part-whole hierarchies.

Behavioral Design Patterns

Examples:

• Command: Encapsulates a request as an object, thereby allowing for parameterization of clients with queues, requests, and operations.
• Iterator: Provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
• Mediator: Reduces coupling between classes by allowing them to communicate through a mediator.
• Observer: Defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified.
• PubSub (Publish-Subscribe): A messaging pattern where senders (publishers) do not program messages to be sent directly to specific receivers (subscribers).
• Visitor: Allows adding further operations to objects without having to modify them.

Architectural Design Patterns

Examples:

• MVVM (Model-View-ViewModel): Facilitates a separation of development of the graphical user interface from the development of the business logic or back-end logic.
• MVC (Model-View-Controller): Separates an application into three interconnected components, allowing for efficient code reuse and parallel development.

Conclusion

Design patterns play a crucial role in the structuring of an application and are invaluable tools for developers. By understanding and implementing these patterns, developers can create more robust, maintainable, and scalable applications.