JBEE is as straightforward to use as possible. In the simplest case all you need to do is to create a new instance of Evaluator and call it's evaluate() method with the desired expression:

System.out.println(new Evaluator().evaluate("1 + 1");

You will either get a result or null if the expression cannot be parsed. If you are interested in why parsing fails, use the evaluateOrThrow() method instead.