import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;

class Ideone
{
    public static void main(String[] args) throws Exception
    {
        ScriptEngine js = new ScriptEngineManager().getEngineByName("JavaScript");
        js.eval("function x(s){return s.replace(/(a)(?!b)\1/gm, 'c');}");
        System.out.println(String.valueOf(((Invocable)js).invokeFunction("x", "aa")));
    }
}