Why isn't ConstantPoolGen final?

Hi!

After my recent performance patch, I have further looked for code that 
could possibly be speed by applying a few optimisations.

Although only a small percentage of total time is spend in ClassGen 
initialisation (about 20% of deserialization and about 10% of combined 
deserialization/serialization time), some speedup may be achieved here.

I was wondering why ConstantPoolGen isn't final, and why the fields 
size, constants and index as well as the method adjustSize are 
protected? Are there actually subclasses out there that depend on their 
contracts implicitly defined by the current implementation?

cheers,
Markus