Decorator Design Pattern
- 1. Decorator Design Pattern Elements of Reusable Object-Oriented Software
- 2. Content 1. Design Patterns 2. Decorator Design Pattern 3. Example I. Class Structure II. Implementation 4. Conclusion 2
- 3. Design Pattern 3 Best practices Solutions to general problems
- 4. Decorator Design Pattern • Attach additional responsibilities to an object dynamically. • Decorators provide a flexible alternative to subclassing for extending functionality. • Wrapping a gift, putting it in a box, and wrapping the box. 4
- 5. Problem You want to add behavior or state to individual objects at runtime. Inheritance is not feasible because it is static and applies to an entire class. 5
- 6. Example 6 Window Window with Vertical Scrollbar Window with Horizontal Scrollbar Window with Border Window with Vertical and Horizontal Scrollbar Window with Vertical and Horizontal Scrollbar and Border
- 7. Class Structure 7 <<interface>> Window + draw() <<class>> MainWindow + draw() <<interface>> WindowDecorator + draw() <<class>> Border <<class>> Vertical SB <<class>> Horizontal SB
- 8. Implementation 8 Window appMainWindow = new BorderDecorator( new HorizontalScrollBarDecorator( new VerticalScrollBarDecorator( new MainWindow( 80, 24 )))); appMainWindow.draw();
- 9. Conclusion • Decorators allow behavior modification at runtime rather than going back into existing code and making changes • The decorator pattern supports the principle that classes should be open for extension but closed for modification 9
- 10. Kanushka Gayan SE intern @ Extrogene Software (Pvt) Ltd kanushkanet@gmail.com 071 879 4546 Thank You!
Editor's Notes
- #2: https://sourcemaking.com/design_patterns/decorator
- #5: Decorator pattern allows a user to add new functionality to an existing object without altering its structure. This type of design pattern comes under structural pattern as this pattern acts as a wrapper to existing class. This pattern creates a decorator class which wraps the original class and provides additional functionality keeping class methods signature intact.
- #7: Suppose you are working on a user interface toolkit and you wish to support adding borders and scroll bars to windows. You could define an inheritance hierarchy like But the Decorator pattern suggests giving the client the ability to specify whatever combination of "features" is desired.
- #8: Suppose you are working on a user interface toolkit and you wish to support adding borders and scroll bars to windows. You could define an inheritance hierarchy like But the Decorator pattern suggests giving the client the ability to specify whatever combination of "features" is desired.