Factory#
Factory patterns are so called creational patterns meaning their intent is to abstract/hide how objects are created. Which in return allows the client to be in independent of how its objects are created.
Factory method#
The factory method pattern delegates the instantiation of objects to a method in either subclasses or a static method. The disadvantage of having the factory method as a static method is it can not be subclassed to change the behavior however you don't need to create an object to make use of the method.
Structure#
classDiagram
Creator <|-- ConcreteCreator
Creator --> ProductInterface
ProductInterface <|-- ConcreteProduct
class Creator{
+someOperation()
+createProduct(): Product
}
class ProductInterface{
}
class ConcreteProduct{
}
class ConcreteCreator{
+createProduct(): Product
returns a ConcreteProduct
}
Example#
Abstract factory#
The factory method pattern delegates the instantiation of object familys to a another object.
Structure#
A big question here is where is the concrete Factory so they can all have acces to it. Often this is done in it's own class
public class CurrentFactory {
private CurrentFactory() { }; // prevents instantiation
private static Factory fac = null;
public static Factory getFactory() { return fac; }
public static void setFactory(Factory f) {
if (f == null) throw new NullPointerException();
fac = f;
}
}
Example#
