/dɪˈzaɪn ˈpætərnz/
noun … “Proven templates for solving common software problems.”
Design Patterns are reusable solutions to recurring problems in software architecture and object-oriented design. They provide templates for structuring code to improve maintainability, scalability, and readability, without prescribing exact implementations. Patterns encapsulate best practices and lessons learned from experienced developers, allowing teams to communicate ideas efficiently using standardized terminology.
Key characteristics of Design Patterns include:
- Reusability: patterns can be adapted across projects and languages while preserving their core intent.
- Abstraction: they provide high-level templates rather than concrete code.
- Communication: developers share complex solutions quickly by naming patterns, e.g., Singleton, Observer, or Factory.
- Scalability: patterns often facilitate extensible and modular designs, enabling easier adaptation to changing requirements.
Categories of Design Patterns commonly used in OOP include:
- Creational: manage object creation, e.g., Singleton, Factory, Builder.
- Structural: organize relationships between objects, e.g., Adapter, Composite, Decorator.
- Behavioral: define interactions and responsibilities, e.g., Observer, Strategy, Command.
Workflow example: A developer implementing a notification system can use the Observer pattern. The Subject maintains a list of subscribers (observers). When an event occurs, the subject notifies all observers, decoupling event generation from response handling. This approach allows adding new notification channels without modifying existing logic.
trait Observer {
def update(message: String): Unit
}
class ConcreteObserver(name: String) extends Observer {
def update(message: String): Unit =>
println(name + " received " + message)
}
class Subject {
private var observers: List[Observer] = List()
def addObserver(o: Observer) => observers = observers :+ o
def notifyObservers(msg: String) => observers.foreach(_.update(msg))
}
val subject = new Subject
val obs1 = new ConcreteObserver("Observer1")
val obs2 = new ConcreteObserver("Observer2")
subject.addObserver(obs1)
subject.addObserver(obs2)
subject.notifyObservers("Update available")Conceptually, Design Patterns are like pre-made blueprints for a building: they guide construction, reduce errors, and ensure that multiple builders can understand and modify the structure consistently. Patterns give a shared vocabulary and strategy for solving recurring problems without reinventing solutions.
See OOP, Scala, Java, Actor Model.