Creational patterns provide object creation mechanisms that increase flexibility and reuse of existing code.
- Factory method: Provides an interface for creating objects in a superclass, but allow subclass to alter the type of objects that will be created.
- Abstract Factory: Lets you produce families of related objects without specifying their concrete classes.
- Builder: Lets you construct complex objects step by step. The patterns allows you to produce different types and representations of an object using the same construction code.
- Prototype: Lets you copy existing objects without making your code dependent on their classes.
- Singleton: Lets you ensure that a class has only one instance, while providing a global access point to this instance.
Structural patterns explain how to asssemble objects and classes into larger structures, while keeping these structures flexible and efficient.
- Adapter: Allow objects with incompatible interfaces to collaborate.
- Bridge: Lets you split a large class or a set of closely related classes into two separate hierarchies - abstraction and implementation - which can be developed independently of each other.
- Composite: Let you compose objects into tree structures and then work with those structures as if they were individual object.
- Decorator: Lets you attach new behaviors to objects by placing these objects inside speical wrapper objects that contain the behaviors.
- Facade: Provides a simplified interface to library, a framework, or any other ocmplex set of classes.
- Flyweight: Let you fit more objects into the available amount of RAM by sharing common parts of state between multiple objects instead of keeping all of the data in each object.
- Proxy: Lets you provide a substitute or placeholder for another object. A proxy controls acces to the original object, allowing you to perform something either before or after the request gets through to the original object.
Behavioral patterns take care of effective communication and assignment of reponsibilities between objects.
- Chain of Responsibility: Lets you pass requests along a chain of handlers. Upon receiving a request, each handler decides either to process the request or to pass it to the next handler in the chain.
- Command: Turns a request into a stand-alone object that contains all information about the request. This transformation lets you pass request as a method arguments, delay or queue a request's execution, and support undoable operations.
- Iterator: Lets you traverse elements of a collection without exposing its underlying representation (list, stack, tree, etc).
- Mediator: Lets you reduce chaotic dependencies between objects. The pattern restricts direct communications between the objects and forces them to collaborate only via a mediator object.
- Memento: Lets you save and restore the previous state of an objet without revealing the details of its implementation.
- Observer: Lets you define subscription mechanism to notify multiple objects about any events that happen to the object they're observing.
- State: Lets an object alter its behavior when its internal state changes. It appears as if the obejct changed its class.
- Strategy: Lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.
- Template Method: Defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure.
- Visitor: Lets you separate algorithms from the object on which they opearte.