1. Usage Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality. [GoF, p175] Client-specified embellishment of a core object by recursively wrapping it. Wrapping a gift, putting it in a box, and wrapping the box. 2. UML class diagram 3. Pros Decorators provide a flexible alternative to […]
1. Usage When sub-system very complex and has many subsystems it make sense to unify access to it by providing single interface called facade. Facade isolate subsystems from direct calls and such way reducing dependency between modules and improve re-usability . 2. UML class diagram 3. Pros It helps to use subsystem as only single […]
1. Usage you need to use many objects lets put 1000-100000. They are similar and related. For example icons of folders and files in Windows. To allow them share similar properties from one side but be ready to be customized we can use Flyweight pattern. Inner proprieties shared by all objects of group called Intrinsic […]
1. Usage Composite is composing tree like structures as single object(container), and let clients to go through such composed objects and regular objects uniformly. Qt Library has implicit support of Composite pattern due to ability to SetParent of QObject. 2. UML class diagram (source: http://www.cs.unc.edu/~stotts/GOF/hires/pat4cfso.htm) Typical Composite Object structure: 3. Pros It makes it easy […]
1. Usage Kind of “2D Abstraction” (or by Rumbaugh “nested generalizations”) both on Interface(Window in example below) and on Implementation(WindowImp). So both Abstraction and Implementation should be extensible by sub-classing.Another name for this pattern is Handle-Body.This Pattern often used in Window Libraries e.g. AWT. Qt library uses this pattern for switching Style at run-time. Reasons […]
1. Usage Proxy pattern in general is Wrapper. Sometimes its hard/impossible to modify real object. For client using Proxy object should be same like using real object as they share same interface. Consider following usage scenarios: Remote Proxy – in distributed communication we create local proxy object which hide all communication with remote object Virtual […]
1. Usage Converts interface of one class which required into another interface which can be called. This pattern also knows as Wrapper. Can be useful with Legacy classes which cannot be changed. It can be implemented 2 ways: Class Adapter: Adapter sub-class required class and at same time implement interface client want to use. Such […]