Design patterns are reusable solutions to common software development problems. They are solutions to recurring problems that have been found to be effective in the past and can be used in a variety of different contexts. In software engineering, design patterns are used to provide a common vocabulary for discussing software architecture and design.
Design patterns are divided into three main categories: Creational, Structural, and Behavioral. Creational patterns focus on how objects are instantiated. Structural patterns concentrate on how classes and objects are arranged to form larger structures. Lastly, Behavioral patterns emphasize how objects communicate and collaborate with each other.
The 23 design patterns commonly implemented in software engineering are: Abstract Factory, Builder, Factory Method, Prototype, Singleton, Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy, Chain of Responsibility, Command, Interpreter, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, and Visitor.
Design patterns provide a unified language for discussing software architecture and design. Knowing and understanding the 23 design patterns can help developers create more flexible and maintainable software applications.