factory method : Java Glossary
©1996-2017 2006-02-21 Roedy Green of Canadian Mind Products
- factory method
A factory is a sort of generic constructor that might produce any of a number of
different kinds of objects. You have to implement it as a static method, rather than a constructor.
In Javadoc, click USE to discover factory methods that
will produce objects of the current class. Often there is no public constructor and
you have to dig around to find the corresponding factory method in some other
class. It is not formally linked to the class it is the factory for.You can implement a factory in several ways:
If you want to give others the ability to add new types to the factory, the
static method pretty well has to fob the work off on a
factory delegate object or objects that can be changed. You can can’t directly
override a static factory method and others would ignore an overridden instance
- Have a big switch and select the right
- Use a Hashtable/HashMap
and .clone() to reproduce pre-initialised exemplar
- use getInstanceOf to create arbitrary objects from
just the class name provided as a String.
You can also use factories to build complicated objects of only a single class
that must be built-in stages, when there are too many parameters to handle
conveniently with a constructor. You want to avoid allowing any malformed or
partly-formed objects loose out into the universe.
Sample Factory Pattern Code
Here is the code for two
simple-minded factories, that illustrate some of the things factories are commonly
- Birth control. Preventing the creation of invalid objects.
- Automatically creating specialised versions of objects.
- Automatic post processing of newly created objects.