Chapter 6_ Using Design Patterns.docx - Introduction to...

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Introduction to Patterns Design Patterns The outline of a reusable solution to a general problem encountered in a particular context Many of them have been systematically documented for all software developers to use A good pattern should: - Be as general as possible - Contains a solution that has been proven to effectively solve the problem in the indicated context Pattern Description Context: General situation in which the pattern applies Problem: Short sentence or two raising the main difficulty Forces: The issues or concern to consider when solving the problem Solution: The recommended way to solve the problem in the given context to balance the forces Antipatterns (Optional): Solutions that are inferior or do not work in this context Related Patterns: (Optional): Patterns that are similar to this pattern References: Who developed or inspired the pattern The Abstraction-Occurrence Pattern Context Occurrence: set a related objects Members of such a set share common information but also different from each other in different ways Problems What is the best way to represent such sets of occurrences in a class diagram? Forces You want to represent the members of each set of occurrences without duplicating the common information

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Solution Antipatterns Square Variant General Hierarchy Pattern Context Objects in a hierarchy can have one or more objects
above them (superiors) and one or more objects below them (subordinates) Some objects cannot have any subordinates Problem How do you represent a hierarchy of objects in which some objects cannot have subordinates. Forces You want a flexible way of representing the hierarchy that prevents certain objects from having subordinates All the objects have many common properties and operations Solutions

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Antipattern The Player-Role Pattern Context A role is a particular set of properties associated with an object in a particular context An object may play different roles in different context Problem How do you best model players and roles so that a player can change roles or possess multiple roles?
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