Factory Vs Prototype - What to use when?

Question

Both Factory & Prototype help in creating objects. When designing a new application:

1. When would you use Factory Pattern over Prototype Pattern?
2. When would you use Prototype Pattern over Factory Pattern?

I am quite confused which one to use where.

I know it can be very much problem specific but is there any general guideline?

Thoughts?

Answer 1

As i see it, although both are creational patterns, factory and prototype patterns are used in different contexts.

Factory pattern is used to introduce loose coupling between objects as the factory will take care of all the instantiation logic hiding it from the clients.

Prototype pattern on the other hand is used when the cost of creating an object is large and it is ok to copy an existing instance than creating a new instance.

Answer 2

I am going to assume you're talking about the Abstract Factory design pattern (which shouldn't be confused with the Factory Method, which is another creational design pattern).

The difference between the two is not too obvious, for they can overlap and be used in a complementary way. Since the prototype creates a clone of itself, including all its properties, it is often created by an abstract factory just once, and then cloned for every necessary object (that will not require having its fields filled again).

Prototype thus avoids unnecessary "new" calls, for the objects are cloned and not created. In most modern OOP languages however, I wouldn't say it's such a big deal. My two cents : if you don't really see the difference, just keep on using the one you're used to implementing (that is, probably the abstract factory).