I am creating a project in Android studio using Java

I have imported "bsh" library in order to use Interpreter class and I added that as a library

here are the statment that I am trying to evaluate the string as a math equation

String value="";

String input = "2+2-2+5";

Interpreter i = new Interpreter();

i.eval("input;");

value = String.valueOf(i.get("input;");

The return value is null I do not why?

Can you help me?