java generics vs dynamically loading class using Class.forName()

Question

Assume I am making a class called Government. Government has members like officers, ministers, departments etc. For each of those members I create an interface, and any specific government defines them as they like.

The main method in the Government class is called Serve(Request req). Assume that the query rate is very large (1000+ queries per second).

To create the government, I can:
1) Use Java generics to write Government<Class Minister, Class Officer, ...> and any specific government implementation needs to create its own Government object in java code, and a main() to have deployable jar.

2) Have a configuration file which specifies the class names of officers, ministers etc., and whenever Serve() is called, it uses Class.forName()and Class.newInstance() to create an object of the class. Any new government just needs to write classes for its members, and the configuration file. There is one single main() for all governments.

From a purely performance point of view - which is better and why? My main concerns are:

a) does forName() execute a costly search every time? Assume a very large universe of classes.

b) Do we miss out on the compiler optimizations that might be performed in case 1 but not in case 2 on the dynamic classes?

As generics shouldn't matter your question boils down to http://stackoverflow.com/questions/647111/newinstance-vs-new — Oleg Mikheev, Dec 15 '11 at 13:29
I agree newInstance() vs new should not matter much. But does forName() matter? Do we need a costly search every time? — Aman, Dec 15 '11 at 13:33
`forName()` should be called just once per class to load it, and not each time you're creating a new instance... — Oleg Mikheev, Dec 15 '11 at 13:44
But if its called everytime it might slow things down noticeably? — Aman, Dec 15 '11 at 13:48
My guess is yes, because it does security checks and some natively implemented logic... — Oleg Mikheev, Dec 15 '11 at 13:51
Okay....I guess it is foolish to call forName() here for every request - so some of the above discussion is academic. It might just be useful to see the scope of compiler optimization. — Aman, Dec 15 '11 at 16:30
`Government` is not remotely valid syntax and I have no idea what you mean here — newacct, Dec 15 '11 at 22:33

Konstantin Pribluda · Accepted Answer · 2011-12-15T13:58:10.837

2

As long as you reuse your goverment object, there is no difference at runtime. Difference isonly at object creation time.

1 & 2 differ in concept - 1 ist hardwired, while 2 is dynamic ( you may even use DI contrainers like spring, guice or pico - basically you proposed to write your own )

As for forName() performance - it is up on classloader ( and also on container ) . MOst of them would cache name resolution results, look up in map - but I can not speak for all

As for optimisations - there are compiler optimisations, and also agressive runtime optiomisations from JIT compilers - they matter more.

edited Dec 15 '11 at 13:58

answered Dec 15 '11 at 13:18

Konstantin Pribluda

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Both design paradigms are useful dependent on the situation. My question was just about performance. – Aman Dec 15 '11 at 13:25
You are not answering from *purely performance point of view* – Oleg Mikheev Dec 15 '11 at 13:28
from purely eprfromance point of view it does not matter. In any case claases will have to be loaded and instantiated. Configurable solution will have some overhead on startupm, but it can be neglected – Konstantin Pribluda Dec 15 '11 at 13:32
@KonstantinPribluda I have modified the original question to be more specific. Can you take a look again? – Aman Dec 15 '11 at 13:47

score 0 · Answer 2 · answered Dec 15 '11 at 22:40

I don't get it. Those two are not alternatives; they are pretty much orthogonal: Generics is a compile-time construct. It is erased and does not translate to anything at runtime. On the other hand, loading classes by calling forName is a runtime thing. One does not affect the other.

If you are using generics, then that means you don't need the class object at runtime, since in generics you don't have access to the class object, unless you pass it in explicitly. If you don't need the class object at runtime, that means you don't need to load it with forName, so that is inconsistent with forName. If you do pass the class object in explicitly, then that means you already have the class object and don't need to load it, also inconsistent with forName.

score 0 · Answer 3 · answered Dec 15 '11 at 22:52

Your description kind of reads like this to me: "I want to use dependency injection, should I roll my own?"

Look into Spring (or Guice by Google). I'll assume Spring.

Create interfaces for stuff and configure which implementation to use for each in Spring.

java generics vs dynamically loading class using Class.forName()

3 Answers3