Behavioral Design Patterns

Chain of Responsibility Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it. Command Encapsulate a request as an object, thereby letting you parametrize clients with different requests, queue or log requests, and support undoable operations. Iterator Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation. Mediator Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently. Memento Without violating encapsulation, capture and externalize an object's internal state so that the object can be returned to this state later. Observer Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. State Allow an object to alter its behavior when its internal state changes. The object will appear to change its class. Strategy Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from the clients that use it. Template method Define the skeleton of an algorithm in an operation, deferring some steps to client subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure. Visitor Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.