Design Pattern(decorator design pattern) and anti pattern
- 1. Presented by Muhammad Arslan Hamza Abbas Aqeel Ahmad Khan Saqib Masood
- 2. Decorator Design Pattern Context Of use Motivation Real Life Example consequences UML Diagram Implementation Anti Patterns Design Patterns
- 3. Design Patterns In software engineering, a design pattern is a general repeatable solution to a commonly occurring problem in software design 12 Decorator
- 4. Structural patterns Design Patterns that ease the design by identifying a simple way to realize relationships between entities.
- 5. The Decorator Pattern Motivation Want to add properties to an existing object. 3 Examples • Add borders or scrollbars to a GUI component • Add headers and footers to an advertisement • Add stream functionality such as reading a line of input or compressing a file before sending it over the wire Intent Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing to extend flexibility
- 6. Use Decorator To add responsibilities to individual objects dynamically without affecting other objects When extending classes is impractical • Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination (this inheritance approach is on the next few slides)
- 7. Suppose there is a Text View GUI component and you want to add different kinds of borders and/or scrollbars to it You can add 3 types of borders Plain, 3D, Fancy and , 1, or 2 two scrollbars Horizontal and Vertical An inheritance solution requires15 classes for one view An Application
- 8. That’s a lot of classes! 1.TextView_Plain 2.TextView_Fancy 3.TextView_3D 4.TextView_Horizontal 5.TextView_Vertical 6.TextView_Horizontal_Vertical 7.TextView_Plain_Horizontal 8.TextView_Plain_Vertical 9.TextView_Plain_Horizontal_Vertical 10.TextView_3D_Horizontal 11.TextView_3D_Vertical 12.TextView_3D_Horizontal_Vertical 13.TextView_Fancy_Horizontal 14.TextView_Fancy_Vertical 15.TextView_Fancy_Horizontal_Vertical
- 9. Consequences(1) More flexibility than static inheritance. responsibilities can be added and removed at run-time simply by attaching and detaching them. Furthermore, providing different Decorator classes for a specific Component class lets you mix and match responsibilities.
- 10. Consequences(2) Avoids feature-laden classes high up in the hierarchy. Offers a pay-as-you-go approach to adding responsibilities. You can define a simple class and add functionality incrementally with Decorator objects. Also easy to define new kinds of Decorators independently.
- 11. Consequences(3) A decorator and its component aren’t identical. From an object identity point of view, a decorated component is not identical to the component itself. Hence you shouldn’t rely on object identity when you use decorators.
- 12. Anti design patterns “An Anti Pattern is a literary form that describes a commonly occurring solution to a problem that generates decidedly negative consequences.” Four type of anti design patterns: Programming anti patterns Methodology anti patterns Design anti patterns Organizational anti patterns