1 / 11

Strategy Pattern

Csci 490 / Engr 596 Special Topics / Special Projects Software Design and Scala Programming Spring Semester 2010 Lecture Notes. Strategy Pattern. This is a set of slides to accompany chapter 8 of Mark Grand’s book Patterns in Java : a catalog of reusable design patterns illustrated with UML

deacon
Télécharger la présentation

Strategy Pattern

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Csci 490 / Engr 596Special Topics / Special ProjectsSoftware Design and Scala ProgrammingSpring Semester 2010Lecture Notes

  2. Strategy Pattern This is a set of slides to accompany chapter 8 of Mark Grand’s book Patterns in Java : a catalog of reusable design patterns illustrated with UML (John Wiley & Sons, 1998) Created: 19 August 2004 Revised: 20 April 2010

  3. Context • Any one of a family of algorithms may do a task • Wish to make then dynamically interchangeable • Invoke only operations on the base class • Delegate creation of the actual subclass object to a special class – factory 1

  4. General Approach • Common interface to family • abstract class/interface • Encapsulate algorithm into implementing (sub)class • Delegate task by using interface 2

  5. Hoilday getHolidays(:Date):String[] Uses 1..* CalendarDisplay Uses 1 0..1 … USHoliday CanadaHoliday CompostiteHoliday Example • CalendarDisplay uses a Holiday instance to determine what holidays fall on each date • Actually use instance of an appropriate subclass • Composite Holiday further delegates to several other subclasses 3

  6. A class in this role provides common way to access operation encapsulated by its subclasses. AbstractStrategy Operation() Uses Client 1 0..1 A class in thisrole delegates an operation to an abstract class or interface. … ConcreteStrategy2 ConcreteStrategy1 Classes in thisrole implement alternative implementations of the operation that the client class delegate. Solution 4

  7. Consequences • Client behavior dynamically determined object by object • Client class simplified • No need to select/implement the alternative behavior • Need way to configure 5

  8. Example CodeClient class CalendarDisplay { private Holiday holiday; private static final String [] noHoliday = new String[0]; … // Private class used to cache information about dates private class DateCache { private Date date; private String[] holidayStrins; DateCache (Date dt) { date = dt; … if (holiday == null) holidayStrings = noHoliday; else HolidayStrings = holiday.getHolidays(date); … } // constructor(Date) }//class DateCache … } //class CalendatDisplay 6

  9. Example CodeAbstractStrategy public abstract class Holiday { protected final static String [] noHoliday = new String[0]; // Return array of strings describing holidays falling on a date // If no holidays fall on the given date, returns a zero length array abstract public String[] getHolidays(Date dt); } // class Holiday 7

  10. Example CodeConcreteStrategy public class USHoliday extends Holiday { … public String [ ] getHolidays(Date dt) { String [ ] holidays = noHoliday; … return holidays; } //getHolidays(Date) } //class USHoliday 8

  11. Acknowledgement This work was supported by a grant from Acxiom Corporation titled “The Acxiom Laboratory for Software Architecture and Component Engineering (ALSACE).” 9

More Related