当类名作为字符串时，转换为未知类型

public class ExampleClass {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Horse hr1 = new Horse();
        Horse hr2 = new Horse();
        Horse hr3 = new Horse();
        Horse hr4 = new Horse();
        Set hrSet = new HashSet();
        hrSet.add(hr1);
        hrSet.add(hr2);
        hrSet.add(hr3);
        hrSet.add(hr4);
        Horse hr;
        String hor = "sher_pkg.Horse";
        callHorse(hrSet,hor);
    }
    public static void callHorse(Set xSet,String clsName){
        try {
            Class hrt = Class.forName(clsName);

            Iterator hritr = xSet.iterator();
            while(hritr.hasNext()){
                exam(hrt.cast(hritr.next()));
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    public static void exam(Object obj){ //I want to use exam(Horse hrr)
        System.out.println(obj);
    }
}
public class ExampleClass {
    public static v