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Design Patterns

Design Patterns. Design Patterns. Fundamental Design Patterns Creational Design Patterns Partitioning Patterns Behavioral Patterns Concurrency Patterns. Fundamental Design Patterns (FDP). Delegation ** Interface Marker Interface Immutable Proxy. FDP - Delegation. Synopsis:

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Design Patterns

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  1. Design Patterns

  2. Design Patterns Fundamental Design Patterns Creational Design Patterns Partitioning Patterns Behavioral Patterns Concurrency Patterns

  3. Fundamental Design Patterns (FDP) Delegation ** Interface Marker Interface Immutable Proxy

  4. FDP - Delegation Synopsis: Delegation is a fundamental method to extend and reuse a classes functionality ( behavior or methods) Context: Allows instances of a class to play multiple roles. Solution: Reuse and extend behavior using delegation

  5. FDP - Delegation class x public void methodforx () { } class y x _x = new x(); …… _x.methodforx ( ) DELEGATION

  6. FDP - Delegation - Example Delegator uses 1 Delegatee 1 Class or Instance Instance

  7. FDP - Delegation - Example 1. checkluggage() 1.1 checkluggage() FlightSegment 1 LuggageCompartment 1 Instance

  8. FDP - Delegation - Example // Instance of this class represent a flight segment. class FlightSegment { LuggageCompartment luggage; /** * Check a piece of luggage * @param piece The piece of luggage to be checked. * @exception LuggageException if piece cannot be checked. */ void checkLuggage(Luggage piece) throws LuggageException { luggage.checkLuggage(piece); } // checkLuggage(Luggage) } // class FlightSegment DELEGATION

  9. Fundamental Design Patterns (FDP) Delegation ** Interface - Allows classes with some similar data to use polymorphism to execute behavior. Marker Interface - used for utilities – allows investigation into class information without knowing they are an instance of a particular class. Immutable – forbids any of an object’s state information to change after the object is created. Proxy - forces method calls to an object indirectly.

  10. Creational Design Patterns Factory Method ** Abstract Factory Builder Prototype Singleton Object Pool **

  11. CDP - Factory Method Synopsis: Need for a class to reuse with arbitrary data types. Reusable class remains independent of the classes it instantiates by delegating the choice of which class to instantiate to another object and referring to the newly created object through a common interface. Context: Creates a framework to support instantiations of various data types.

  12. CDP - Factory Method Solution: Proxy object and the service providing object must either be instances of a common super class or implement a common interface.

  13. CDP - Factory Method - Example You have an application such as MS Office. You want to perform some common functions with all the files. Example of common functions might be open file, save file, etc. The only difference is that the functions are done on different file types such as word doc files, excel xls files and PowerPoint ppt files. You could write several independent functions for each of the different types but the code would be very similar with only the data type as a difference. Factory method allows you to build a framework for common functions with only a few classes that reuse methods for each type.

  14. CDP - Factory Method - Example Manage Doc Files doc file commands Manage Xls Files xls file commands Manage Ppt Files ppt file commands file commands Manage Files Make one Function

  15. CDP - Factory Method - Example edits Document 1 Application * MyDocument May be doc, xls, or ppt.

  16. CDP - Factory Method - Example Suppose you have a process which reads and writes a DataStream to a socket. Write to Socket stream string Socket Read from Socket stream string Socket But you also wish to have strings in which you encrypt the data. And you write an encrypted DataStream and read back an encrypted Data Stream decrypt it.

  17. CDP - Factory Method - Example encrypted stream encrypted string Write to Encrypted Socket EncryptedSocket encrypted stream string encrypted string Encrypt Data Write to Encrypted Socket EncryptedSocket encrypted stream encrypted string decrypted string Read from Socket Decrypt Data Socket But now you realize that there are several different encryption algorithms and codes you wish to use.

  18. CDP - Factory Method - Example The process to encrypt differs in using many different different algorithms (function/method) and type of string output must be written for each type. encrypted stream encrypted String #1 Encrypt Data Write to Encrypted Socket string EncryptedSocket algorithm # 1 encrypted stream encrypted String #2 Encrypt Data Write to Encrypted Socket string EncryptedSocket algorithm # 2 encrypted stream encrypted String #n Encrypt Data Write to Encrypted Socket string EncryptedSocket algorithm # n

  19. CDP - Factory Method - Example The factory pattern allows you to have a framework that will handle any type of algorithm and encrypted data. concrete product encrypted stream encrypted String Encrypt Data Write to Encrypted Socket string EncryptedSocket algorithm # 1 algorithm # n algorithm # 2

  20. CDP - Factory Method - Example Socket Socket 4 6 Product encrypt, decrypt 1 Encryption EncryptedSocket EncryptedSocket 1 * Creation Requester DESEncryption 1 5 * Transcription Concrete Product * creates 1 creates 1 EncryptionFactory 3 Factory * requestCreation EncryptionFactoryIF Interface 2

  21. CDP - Object Pool Synopsis: Manages reuse of objects when a type of object is expensive to create or only limited number needed. Context: You wish to limit access to a resource. Solution: Create a reusable class to collaborate with other objects for a limited amount of time. Create a reusable pool to manage reusable objects for use by client objects.

  22. CDP - Object Pool Suppose you have a database systems that need to allow only a limited number of accesses to the database at one time. Allow Database Access database access requested database access You must write a counting semaphore to protect this resource from having more than the limited access.

  23. CDP - Object Pool manage objects Client ReusablePool Reusable Pool uses Reusable

  24. Partitioning Patterns Layered Initialization ** Filter Composite

  25. PP - Layered Initialization Synopsis: You need multiple implementations with common logic in super and specialized in subs. However the common logic decides which specialized subclass to create. Therefore layered initialization encapsulates common and specialized logic to create the multiple implementations.

  26. PP - Layered Initialization Context: You have a piece of logic that requires partial execution prior to determining which subclass methods might be used. You need to layer the initializations of the objects to process the complex logic or complex data.

  27. PP - Layered Initialization Forces: A specialized class must be chosen to process complex data. Constructor of the specialized classes and their sub classes are invoked after it has been decided which specialized class to instanciate. Solution: Essence of this pattern is to layer the initializations of the objects participating in the pattern.

  28. PP - Layered Initialization • Objects that performs logic common to all cases is initialized • Initialization concludes by determining the class to instantiate • Specialized class constructor performs next layer of initialization logic. • After all initialization, one top-level object exist for logic • If method needs more specialized logic, it calls method one layer down • Consequences: • Complexity of initialization of objects using data requires analysis before initialization can proceed.

  29. PP - Layered Initialization Suppose you have a business rule engine which must select a type of database on which to query to resolve issues in the rule base. Perform Oracle Query Oracle query trigger to resolve business rule query request Select Database Perform DB2 Query Resolve Business Rules DB2 query n query Perform n Query You cannot perform query until you know what type of database

  30. PP - Layered Initialization You need to initialize the database prior to query. Initialize Database Perform Oracle Query Oracle query trigger to resolve business rule query request Select Database Perform DB2 Query Resolve Business Rules DB2 query n query Perform n Query

  31. PP - Layered Initialization request creation creates ServiceImpFactoryIF DataQueryFactoryIF DataQuery ServiceImpFactory uses DataQueryImplFactory Service OracleQuery DB2Query ….. ServiceImpIIF DataQueryImplIF Data Query factory method object appears like this.

  32. Behavioral Patterns Chain of Responsibility State Command Null Object Little Language Strategy ** Mediator Template Method Snapshot Visitor Observer **

  33. BP - Observer REDO Suppose you have a process which reads and writes a DataStream to a socket. Write to Socket stream string Socket Read from Socket stream string Socket But you also wish to have strings in which you encrypt the data. And you write an encrypted DataStream and read back an encrypted Data Stream decrypt it.

  34. BP - Observer edits Document 1 Application * MyDocument May be doc, xls, or ppt.

  35. Concurrency Patterns Single Threaded Execution Guarded Suspension Balking Scheduler Read/Write Lock Producer-Consumer Two-Phase Termination

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