MyMathQuiz_UI/src/question/MiddleQuestionGenerator.java

package question;

import java.util.Random;

public class MiddleQuestionGenerator implements QuestionGenerator {
    private static final Random random = new Random();
    private final QuestionGenerator primaryGenerator = new PrimaryQuestionGenerator();

    @Override
    public Question generateQuestion() {
        Question q = primaryGenerator.generateQuestion();
        if (random.nextBoolean()) {
            return new Question(q.getQuestion() + " ^ 2", evaluate(q.getQuestion() + "^2"));
        } else {
            return new Question("√" + q.getQuestion(), evaluate("Math.sqrt(" + q.getQuestion() + ")"));
        }
    }

    private String evaluate(String expr) {
        try {
            javax.script.ScriptEngineManager mgr = new javax.script.ScriptEngineManager();
            javax.script.ScriptEngine engine = mgr.getEngineByName("JavaScript");
            return String.valueOf(engine.eval(expr.replace("^", "**")));
        } catch (Exception e) {
            return "?";
        }
    }
}