Programming

Sounds like you’re thinking more about the builder pattern.

Eh? How's that work. I'm not going to sit here and say there isn't too many factories in Java but as a concept it's extremely useful. You hand off a "factory" to something which actually creates the object. This is really useful in for example serialization. How so? You could register factories (mapped to some sort of ID) which get passed the serialized data and return some sort of created object. Now the core serialization code doesn't know nor care how exactly any particular type gets serialized. Pretty nifty huh?

Some languages have better ways to encapsulate this functionality but that's what the factory concept is

Consider the following: You have a class A that has a few dependencies it needs. The dependencies B and C never change, but D will generally be different for each time the class needs to be used. You also happen to be using dependency injection in this case. You could either:

• Inject the dependencies B and C for any call site where you need an instance of A and have a given D, or
• Create an AFactory, which depends on B and C, having a method create with a parameter D returning A, and then inject that for all call sites where you have a given D.

This is a stripped example, but one I personally have both seen and productively used frequently at work.

In this case the AFactory could practically be renamed PartialA and be functionally the same thing.

You could also imagine a factory that returns different implementations of a given interface based on either static (B and C in the previous example) or dynamic dependencies (D in the previous example).