Loop to handle many field condition statements

I have some code that works great in my Bean class that looks like the
below where I have around 15 fields. For example I condensed it to 2
fields:

//bean model part
HashMap errors = new HashMap();
String firstname = "Joe";
String lastname = "Miller";

    if (firstname.equals(""))
    {
        errors.put("firstname","missing firstname".);
    }
    if (lastname.equals(""))
    {
        errors.put("lastname","missing lastname");
    }

//Each field is then called like this in a View page:
errors.get("firstname"));
errors.get("lastname"));Anyway I can create a loop to go through all
15 fields or how is the best way to do this??

//use Array or Iterator or List or what to get the 15 fields then
loop?
for(int i= 0;i < 15;i++)
{
   /*
   how would I make this part work?
   if (firstname.equals(""))
    {
        errors.put("firstname","missing firstname".);
    }
    if (lastname.equals(""))
    {
        errors.put("lastname","missing lastname");
    }
    /*
}

Please advise.