this repo contains implementations of various design patterns in java, mostly inspired by christopher okhravi's videos, with a few extras pulled from other sources like mosh hamedani’s work.
below are the definitions of key design patterns from "design patterns: elements of reusable object-oriented software" by erich gamma, richard helm, ralph johnson, and john vlissides (the "gang of four"):
- purpose: provide a way to create related objects without specifying their exact classes.
- roles:
AbstractFactory,ConcreteFactory,AbstractProduct,ConcreteProduct.
- purpose: let incompatible interfaces work together by converting one interface into another that clients expect.
- roles:
Target,Adapter,Adaptee.
- purpose: separate an abstraction from its implementation so both can change independently.
- roles:
Abstraction,RefinedAbstraction,Implementation,ConcreteImplementation.
- purpose: turn a request into an object so you can queue it, log it, and support undo operations.
- roles:
Command,ConcreteCommand,Receiver,Invoker,Client.
- purpose: arrange objects into tree structures to represent whole-part relationships, so you can treat them all uniformly.
- roles:
Component,Leaf,Composite.
- purpose: add responsibilities to an object dynamically, as an alternative to subclassing.
- roles:
Component,ConcreteComponent,Decorator,ConcreteDecorator.
- purpose: simplify interactions with a system by providing a unified interface to its more complex subsystems.
- roles:
Facade,Subsystemclasses.
- purpose: let subclasses decide which object to create, instead of having the parent class specify the exact class.
- roles:
Creator,ConcreteCreator,Product,ConcreteProduct.
- purpose: provide a way to sequentially access elements of a collection without exposing the underlying structure.
- roles:
Iterator,ConcreteIterator,Aggregate,ConcreteAggregate.
- purpose: capture an object’s internal state without exposing its details, so it can be restored later.
- roles:
Memento,Originator,Caretaker.
- purpose: use a default object when the real object is missing, to avoid null references.
- roles:
AbstractObject,RealObject,NullObject.
- purpose: automatically notify and update dependents when an object changes state.
- roles:
Subject,Observer,ConcreteSubject,ConcreteObserver.
- purpose: provide a stand-in for an object, controlling access to it.
- roles:
Proxy,Subject,RealSubject.
- purpose: ensure a class only has one instance, and provide a way to access it globally.
- roles:
Singleton.
- purpose: change an object’s behavior based on its internal state.
- roles:
Context,State,ConcreteState.
- purpose: define a set of interchangeable algorithms, allowing clients to switch between them.
- roles:
Strategy,Context,ConcreteStrategy.
- purpose: define the overall structure of an algorithm, while allowing subclasses to fill in specific steps.
- roles:
AbstractClass,ConcreteClass.