Behavioral patterns

Passes a request along a chain of handlers; each decides to process it or pass it on.

Turns a request into a stand-alone object containing all information about the request.

Defines a grammar for a simple language and an interpreter that evaluates sentences in it.

Traverses elements of a collection without exposing its underlying representation.

Reduces chaotic dependencies between objects by making them communicate through a mediator object.

Saves and restores an object's previous state without revealing its implementation.

Defines a subscription mechanism that notifies multiple objects about events in the object they observe.

Lets an object alter its behaviour when its internal state changes, as if it changed its class.

Defines a family of algorithms, puts each in its own class, and makes them interchangeable.

Defines the skeleton of an algorithm in a base class and lets subclasses override specific steps.

Separates algorithms from the objects on which they operate.