DESIGN PATTERNS -BEHAVIORAL PATTERNS WATTANAPON G SUTTAPAK Software Engineering, School of Information Communication Technology, University of PHAYAO 1

จุดประสงค์การเรียนรู้  เข้าใจรูปแบบของแบบรูปการออกแบบทั้ง 12 ประเภท  ประยุกต์ใช้แบบรูปการออกแบบทั้ง 12 ประเภทได้ 2

BEHAVIORAL PATTERNS communication between object 1.Chain of Responsibility 2.Command 3.Interpreter 4.Iterator 5.Mediator 6.Memento 7.Observer 8.State 9.Null Object(new) 10.Strategy 11.Template Method 12.Visitor

CHAIN OF RESPONSIBILITY PATTERN This pattern creates a chain of receiver objects for a request decouples sender and receivers of a request base on type of request each receiver contains reference to another receiver. If one object cannot handle the request then it passes the same to the next receiver and so on. 4

CHAIN OF RESPONSIBILITY PATTERN 5

6

7 Result

COMMAND Passing data(object) to invoker object. Invoker object pass the command to the corresponding object The object executes the command. 8

COMMAND 9

10

COMMAND 11 Result

INTERPRETER Evaluate language grammar or expression. Use in SQL parsing, symbol processing engine etc. 12

INTERPRETER 13

INTERPRETER 14

INTERPRETER 15 Result

ITERATOR Iterator pattern is very commonly used design pattern in Java and.Net programming environment. This pattern is used to get a way to access the elements of a collection object in sequential manner without any need to know its underlying representation. 16

ITERATOR 17

ITERATOR 18

ITERATOR 19 Result

MEDIATOR Used to reduce communication complexity between objects(classes) a mediator class which normally handles all the communications between different classes and supports easy maintainability of the code by loose coupling Ex.Chat Room multiple users can send message to Chat Room Chat Room show the messages to all users 20

MEDIATOR 21

MEDIATOR 22 Result

MEMENTO Restore state of an object to a previous state. Ex. Memento there are 3 classes : Memento, Originator and CareTaker. Memento contains state of an object to be restored. Originator creates and stores states in Memento objects. Caretaker object which is responsible to restore object state from Memento. 23

MEMENTO 24

MEMENTO 25

MEMENTO 26 Result

OBSERVER Case : one to many relationship between objects Such as if one object is modified, its dependent objects are to be notified automatically. Implementation There are 3 actor classes : Subject, Observer and Client Subject, an object having methods to attach and de-attach observers to a client object Client extending the abstract class the Observer. 27

OBSERVER 28

OBSERVER 29

OBSERVER 30 Result

OBSERVER 31

STATE 32 a class behavior changes based on its state.

STATE 33

STATE 34 Result

NULL OBJECT 35 Checking NULL object instance.

NULL OBJECT 36

NULL OBJECT 37 Result

STRATEGY 38 Problem : various objects was called in same method.

STRATEGY 39

STRATEGY 40 Result

TEMPLATE 41 Create abstract class : template to execute its methods.

TEMPLATE 42

TEMPLATE 43 Result

VISITOR Visitor class changes the executing algorithm of an element class. Execution algorithm of element varies to visitor varies Element object accept the visitor object so that visitor object handles the operation on the element object. 44

VISITOR 45

VISITOR 46

VISITOR 47 Result

VISITOR 48 ComputerPartVisitor can it be removed? but why not? Do you remember Couple and Cohesion?