使用Lambda表达式遍历lteratot,为啥obj会报错

ublic static void main(String args[]){
Collection books=new HashSet();
books.add("疯狂讲义");
books.add("讲义");
Iteratoar it=books.iterator();
it.forEachRemaining(obj -> System.out.println("元素"+obj));
}

 Iteratoar<Object> it=books.iterator(); 看看

http://www.howsoftworks.net/java-api/java-util/spliterator_foreachremaining.html