The SOLID principles are the fundamental guidelines in object-oriented design.
They are high-level concepts that help you develop better software.
They are neither rules nor laws, but they help you think of possible scenarios/outcomes in advance.
GoF Design Patterns are divided into three categories:
Creational: The design patterns that deal with the creation of an object.
Structural: The design patterns in this category deals with the class structure such as Inheritance and Composition.
Behavioral: This type of design patterns provide solution for the better interaction between objects, how to provide lose coupling, and flexibility to extend easily in future.
Creational Design Patterns
| Pattern Name | Description |
|---|---|
| Singleton | The singleton pattern restricts the initialization of a class to ensure that only one instance of the class can be created. |
| Factory | The factory pattern takes out the responsibility of instantiating a object from the class to a Factory class. |
| Abstract Factory | Allows us to create a Factory for factory classes. |
| Builder | Creating an object step by step and a method to finally get the object instance. |
| Prototype | Creating a new object instance from another similar instance and then modify, according to our requirements. |
Structural Design Patterns
| Pattern Name | Description |
|---|---|
| Adapter | Provides an interface between two unrelated entities so that they can work together. |
| Composite | Used when we have to implement a part-whole hierarchy. For example, a diagram made of other pieces such as circle, square, triangle, etc. |
| Proxy | Provide a surrogate or placeholder for another object to control access to it. |
| Flyweight | Caching and reusing object instances, used with immutable objects. For example, string pool. |
| Facade | Creating a wrapper interfaces on top of existing interfaces to help client applications. |
| Bridge | The bridge design pattern is used to decouple the interfaces from implementation and hiding the implementation details from the client program. |
| Decorator | The decorator design pattern is used to modify the functionality of an object at runtime. |
Behavioral Design Patterns
| Pattern Name | Description |
|---|---|
| Template Method | used to create a template method stub and defer some of the steps of implementation to the subclasses. |
| Mediator | used to provide a centralized communication medium between different objects in a system. |
| Chain of Responsibility | used to achieve loose coupling in software design where a request from the client is passed to a chain of objects to process them. |
| Observer | useful when you are interested in the state of an object and want to get notified whenever there is any change. |
| Strategy | used when we have multiple algorithm for a specific task and client decides the actual implementation to be used at runtime. |
| Command | used to implement lose coupling in a request-response model. |
| State | used when an Object change it’s behavior based on it’s internal state. |
| Visitor | used when we have to perform an operation on a group of similar kind of Objects. |
| Interpreter | defines a grammatical representation for a language and provides an interpreter to deal with this grammar. |
| Iterator | used to provide a standard way to traverse through a group of Objects. |
| Memento | is used when we want to save the state of an object so that we can restore later on. |
Gangs of Four design patterns lay the foundation of core design patterns in programming.
There are many other design patterns built on top of these patterns for specific requirements.