Creational Patterns : Simple Factory

Properties:

-          Hides details of class instance creation and actual class implementation. This allows easy replacement of class implementation and gives flexibility to change the way new instance construction  is done.

-          Creates and abstraction layer between client code and object needs to be created, thus facilitates loose coupling.

-          Client provides attributes of the object it needs to create and defers instantion to factory. It is not obligatory to supply any attributes though.

-          Factory creates a suitable class instance according to attributes supplied. 

-          The problem with Factory pattern is when a new implementation is added Factory class needs to be modified which vilotaes the open-closed* principle.

[*]http://en.wikipedia.org/wiki/Open/closed_principle

Implementation:

-          Factory class has method named createXYZ which takes necessary arguments.

-          createXYZ method creates an concrete XYZ instance and retuns to client.

-          Client uses returned XYZ instance without ever knowing actual concrete class used.

Java Standard Library Implementations:

-          Javax.swing.PopupFactory

Example Usage:

PopupFactory factory = PopupFactory.getSharedInstance();

// createXYZ method

// Popup implementation may be one of LightWeightPopup,

// MediumLightWeightPopup, HeawyLightWeightPopup implementations.

Popup popup = factory.getPopup(owner, contents, x, y);

popup.show();

// Some logic.

...

popup.hide();