Try something like this:

public boolean checkNull() throws IllegalAccessException {
    for (Field f : getClass().getFields())
        if (f.get(this) != null)
            return false;
    return true;            
}

Although it would probably be better to check each variable if at all feasible.

Try something like this:

public boolean checkNull() throws IllegalAccessException {
    for (Field f : getClass().getDeclaredFields())
        if (f.get(this) != null)
            return false;
    return true;            
}

Although it would probably be better to check each variable if at all feasible.