Behavioral patterns behavior patterns Summary

ArticleDirectory

• I. general concept
• Ii. Classification

I. general concept

Behavioral patterns
Chain of resp.	A way of passing a request between a chain of Objects
Command	Encapsulate a command request as an object
Interpreter	A way to include language elements in a program
Iterator	Sequentially access the elements of a collection
Mediator	Defines simplified communication between classes
Memento	Capture and restore an object's internal state
Observer	A way of changing Ying change to a number of classes
State	Alter an object's behavior when its State Changes
Strategy	Encapsulates an algorithm inside a class
Template Method	Defer the exact steps of an algorithm to a subclass
Visitor	Defines a new operation to a class without change

Ii. Classification

Based on its features, it is divided into three types:

1. Four models for decoupling sender and receiver:

Command mode:Decouple is the object that calls a command and the object that executes the command. The object that calls the command has no idea about the object that executes the command and the specific method of execution, only the interfaces that are executed are known (through the abstract class interface of command ). You can change the called command at runtime by using different command objects.
Observer mode:It is also called publish-subscribe. In this mode, multiple observers (subscriber subscribers) subscribe to an object. That is to say, when this object changes, all observers should be notified to maintain the data consistency of the observer. In this mode, you can add or delete the observer (subscriber) at any time ).
Mediator mode:Interaction between all objects must be performed through mediator. Each object does not need to know each other, but only needs to know mediator.
Chain of responsibility: decouple the sender and consumer of the command, so that the request is transmitted along the sender to the consumer er

2. encapsulation:

Find and encapsulate the changes. Find out the differences between objects and use these differences as virtual functions of abstract classes, that is, interfaces. For example, the abstract class is a, and the actual classes are A1 and A2.

Object clustering is preferred, rather than class inheritance. Use aggregation to use these objects. If B wants to use a, a pointer of A is used as a member of the class, and then the interface of A is called. In this way, B does not need to know which method A calls the virtual function, which is determined by the actual object type of a at runtime.

Strategy Mode:DifferentAlgorithmAs
State mode:Use different States as

3. Others:

Visitor:In a structure (usually a composite structure), each subclass has a series of operations for this subclass, and these operations often change, the operation (function) in the entire class hierarchy is required) all changes. In this case, the visitor mode is used to make each operation a separate class.

Template Method:The steps of an algorithm are fixed, but some of the steps are implemented based on the specific subclass.
Memento:You need to save the state of an object, but do not want to expose its interface. Use a memento object to store its State and restore its state as appropriate.
Iterator:Traverse a structure (composite structure)
Interpreter:Parse a Language Structure