1.迭代遍历：   
Set<String> set = new HashSet<String>();   
Iterator<String> it = set.iterator();   
while (it.hasNext()) {   
  String str = it.next();   
  System.out.println(str);   
}   
   
2.for循环遍历：   
for (String str : set) {   
      System.out.println(str);   
}   
   
   
优点还体现在泛型 假如 set中存放的是Object   
   
Set<Object> set = new HashSet<Object>();   
for循环遍历：   
for (Object obj: set) {   
      if(obj instanceof Integer){   
                int aa= (Integer)obj;   
             }else if(obj instanceof String){   
               String aa = (String)obj   
             }   
              ........   
}