Gangs of Four Design Patterns is the collection of 23 design patterns from the book “Design Patterns: Elements of Reusable Object-Oriented Software”.
Singleton – Ensure that a class has exactly one copy and provide a global access point to it
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.
Adapter – Provides an interface between two unrelated entities so that they can work together.
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.
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.
Facade – Creating a wrapper interfaces on top of existing interfaces to help client applications.
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.
Template Method – used to create a template method stub and defer some of the steps of implementation to the subclasses.
Strategy – Strategy pattern is used when we have multiple algorithm for a specific task and client decides the actual implementation to be used at runtime.
Command – Command Pattern is used to implement lose coupling in a request-response model.
Memento – The memento design pattern is used when we want to save the state of an object so that we can restore later on.
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.
State – State design pattern is used when an Object change it’s behavior based on it’s internal state.
Iterator – used to provide a standard way to traverse through a group of Objects.
Visitor – Visitor pattern is 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.