How to make static varaible in Appian

You can create constants in Appian. I think this would be the best matching substitute.

When coming from Java, be aware that Appian expressions is a functional programming language and you might have to adjust your way of problem solving a bit.

docs.appian.com/.../Expressions.html

I dont think thats possible, the only way to do something similar is restrict down to one group the security for the constant, but that is very risky and does not follow the best practices.