HashMap 遍历

   entrySet://遍历一次将key和value值放入entry

 Map map = new HashMap();
    Iterator iter = map.entrySet().iterator();
    while(iter.hasNext()){
        Map.Entry entry =(Map.Entry)iter.next();
        Object key=entry.getKey();
        Object val=entry.getValue();
    }

keySet://遍历了2次，转为iterator时候一次，取key对应的value值时遍历一次

Map map = new HashMap();
    Iterator iter = map.keySet().iterator();
    while(iter.hasNext()){
         Object key=iter.next();

         Object val=map.get(key);       

    }