Template Method Design Pattern

Template Method Pattern ~ Mother of all frameworks ~ Srikanth P Shreenivas [email_address] http://www.srikanthps.com

Game Console for playing Pool Slide public class Pool { aTypicalGamingSession() { startup(); retrieveLastSavedState(); displayPoolTable(); while (not exit) { acceptUserInput(); redrawTheTable(); } printWinner() saveUserScore; updateHighScores; } }

Game Console – More games Slide ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Game Console – What’s common? Slide ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Game startGame() { retrieveLastSavedState(); displayGame(); while (not exit) { reactToUserControl(); } saveGame(); printWinner(); } Abstract displayGame(); Abstract reactToUserControl(); Delegate game specific behavior to derived classes, while controlling the main game behavior in base class. Common Behavior Game-specific Behavior Chess displayGame() { displayChessBoard(); } reactToUserControl() { moveThePiece(); } Pool displayGame() { displayPoolTable(); } reactToUserControl() { strikeWithCueBall(); }

Template Method Pattern Slide ,[object Object],[object Object],[object Object],[object Object],[object Object],ConcreteClass 2 step1() { } step3OptionalStep() { //diff. implementation } Algorithm() { step1(); step2MustAlwaysDoThis(); step3OptionalStep(); step4finalStep(); } Abstract step1(); Final step2MustAlwaysDoThis() { } step3OptionalStep() { //Default code } Final step4FinalStep() { } Base Class ConcreteClass 1 step1() { }

Inversion of control ,[object Object],[object Object],Slide Hollywood Principle ,[object Object],[object Object],[object Object],[object Object]

Servlets – A case study for IoC ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Slide

Servlets – IoC and Template Method Pattern ,[object Object],[object Object],[object Object],[object Object],Slide Servlet Container’s Hollywood Principle: Don’t call me, I will call you (servlet) !!! (whenever I hear from a browser) Servlet’s Template Method: Let me have the control of algorithm and let me deal with HTTP, you (Developer) just respond with some meaningful action when I call your methods.

“ Mother of all frameworks”….How? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Slide

Ways of Extending Classes (and Frameworks) ,[object Object],[object Object],[object Object],[object Object],Slide

Example of Strategy Pattern Slide Use Strategy to plug-in a different implementation. CRT print() { print on console’s monitor } PaperPrinter print() { printOnLaserPrinter(); } Game void startGame() { … printer.printWinner(); … } Printer printer; Printer print()

Template Method Design Pattern

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