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A singleton pattern is used to allow the creation of only a single object of a specific
class. This is achieved by making the constructor private or protected and using a
static method to instantiate the class. In versions of PHP prior to version 5, we are
unable to enforce this restriction.
Many of the Joomla! classes use a pseudo-singleton pattern to allow us to instantiate
and access objects. To achieve this, Joomla! often uses a static method called
getInstance(); in some cases JFactory acts as a pass through for this method.
Classes that implement this method are not always intended to be singleton classes.
We can think of them as being a hierarchy in how we instantiate objects. We should
use these methods in order of priority: JFactory method, getInstance() method,
normal constructor (new).
If you're unsure how a specific class implements a getInstance()
method, you should check the official API reference at
http://api.joomla.org. getInstance() and JFactory methods
always return references; always use the =& assignment operator to
prevent copying of objects.


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