CHAPTER 08 REUSABILITY AND PORTABILITY

Categories of Design Patterns● 23 standard design patterns● Divided into three categories● Creational patterns — Solve design problems by creatingobjects• E.g., abstract factory pattern● Structural patterns — Solve design problems by identifying asimple way to realize relationships between entities• E.g., Adapter pattern and bridge pattern● Behavioral patterns — Solve design problems by identifyingcommunicational patterns between objects• E.g., iterator pattern● Other lists and categories proposed: Not widely accepted● Figure 8.12Categories of Design PatternsStrengths and Weaknesses of Design Patterns● Strengths● Promote reuse by solving a general design problem● Provide high-level documentation of design● Implementations exist: No need to code or document thoseparts● If a maintenance programmer is familiar: Easier tocomprehend the program● Research into automated detection of design patterns● Weaknesses● Use of design patterns may be an indication of the languagenot being powerful enough● No systematic way to determine when and how to apply designpatternsStrengths and Weaknesses of Design Patterns● For maximal benefits, multiple interacting patterns areemployed● Impossible to retrofit patterns to an existing softwareproduct● Overall● Weaknesses of design patterns are outweighed by theirstrengths● Once research to formalize and automate design patternssucceeds: Patterns will be easier to use