OSS
Behavioral - Observer/Event-Subscriber/Listener
- lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.
- The Observer pattern suggests that you add a subscription mechanism to the publisher class so individual objects can subscribe to or unsubscribe from a stream of events coming from that publisher.
- this mechanism consists of 1) an array field for storing a list of references to subscriber objects and 2) several public methods which allow adding subscribers to and removing them from that list.
Behavioral - State
lets an object alter its behavior when its internal state changes. It appears as if the object changed its class. extract all state-specific code into a set of distinct classes. As a result, you can add new states or change existing ones independently of each other, reducing the maintenance cost.
Behavioral - Strategy
lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable. take a class that does something specific in a lot of different ways and extract all of these algorithms into separate classes called strategies.
Behavioral - Template Method
defines the skeleton of an algorithm in the superclass but lets subclasses override specific steps of the algorithm without changing its structure. break down an algorithm into a series of steps, turn these steps into methods, and put a series of calls to these methods inside a single template method. The steps may either be abstract, or have some default implementation. To use the algorithm, the client is supposed to provide its own subclass, implement all abstract steps, and override some of the optional ones if needed
Behavioral - Visitor
lets you separate algorithms from the objects on which they operate. The Visitor pattern suggests that you place the new behavior into a separate class called visitor, instead of trying to integrate it into existing classes. The original object that had to perform the behavior is now passed to one of the visitor’s methods as an argument, providing the method access to all necessary data contained within the object.