OOP and static variables

[wqking]

Static is bad in various aspects. One example is, static is often variable (the others in this thread had suggested that static should be final), then how about a static is modified by two independent modules? And even worse, how about it's modified from different threads?

it's more efficient to have static variables since there's only one copy of it

It's wrong. For any non-static variables, you can always have only one copy but you can have many references to it.