Question

Why do people default to DI vs a global factory with a hashmap that maps interfaces/abstracts to classes? It would seem this is a higher performance solution to the problem no?

All the things mentioned so far in this thread can be provided by a global factory with a method like:

TestGlobalFactory implements GlobalFactoryI
ProductionGlobalFactory implements GlobalFactoryI //configures classes to interfaces

protected GlobalFactoryI gf=GlobalFactoryFactory.getInstance(); //only singleton used in app, specifies which GlobalFactory to use

protected SportsCarI mySportsCar=gf.new("sportsCarI",constructorVar1,constructorVar2);

The above would be much faster than recursive reflection to detect DI instances.

However I admittedly prefer the convention of DI as it ends up being fewer characters and greater flexibility with the option of third party containers.

artima.com/forums/flat.jsp?forum=106&thread=238700

Regardless DI, is the superior approach as it has the containers written to specify which implementation belongs in which class. With Service Locator one would actually have to do gf.new(“thisClass”,”sportsCarI”,constructor1)

Answer 1

The main advantage of dependency injection over a factory-based approach is not performance. Its main advantage is testability. The whole point of DI is to be able to inject mock dependencies to implement the unit tests of a component. Doing it with a factory is much more painful.