Yeah it's damage mapping.

If you know the largest rectangle which needs updating then you can just unlock() that sized area.

As to final ( Sorry I shouldn't have capped the F ),

public final class myClass{

}

Gives a minor speed increase as it stops the class being dynamic. You can also use it on methods too, but I've got to be honest I've never felt the need to push things that far.
I mainly just use it on particle classes, where I'll be running lots of instances.

Squize.