public static void main(String[] args) {
        Map map = new HashMap();
        map.put("邓超", "孙俪");//替换
        map.put("王宝强", "马蓉");//ok
        map.put(null, "刘亦菲");//pl
        map.put("鹿晗", null);//ok
        map.put("lu汉", "刘亦菲");
        map.put("沫年", "刘亦菲");//ok
        System.out.println(map);

        //第一组：先取出所有的Key，通过键值对取出相应的Value
        Set keyset = map.keySet();
        System.out.println("======I=====");
        for (Object key : keyset) {
            System.out.println(map.get(key));//这个取出的是Value
        }
        for (Object key : keyset) {
            System.out.println(key);//这个取出的是键值
        }
        //迭代器
        System.out.println("======itit======");
        Iterator ito = map.keySet().iterator();
        while(ito.hasNext()){
            Object key = ito.next();
//            System.out.print(key+" ");//输出key的值
            System.out.print(map.get(key)+" ");//输出key的value
        }

        System.out.println("\n===============");

        //第二组：把所有的values取出
        Collection values = map.values();
        System.out.println("======第1组增强for循环======");
        for(Object obj: map.values()){
            System.out.print(obj +" ");
//            System.out.print(values +" ");//可以直接输出values的值
        }

        System.out.println("\n======第2组增强for循环======");
        Iterator ito2 = values.iterator();
        while(ito2.hasNext()){
            System.out.print(ito2.next()+" ");
        }

        System.out.println("=======第三组增强for=======");
        Set entrySet = map.entrySet();
        System.out.println("=========EntrySet的for增强============");
        for (Object entry :entrySet) {
            Map.Entry m = (Map.Entry) entry;
            System.out.print(m.getValue()+" ");
        }

        System.out.println("\n==========迭代器===========\n");
        Iterator ito3 = entrySet.iterator();
        while(ito3.hasNext()){
          Object entry = ito3.next();
            System.out.println(entry);//HashMap$Node ---实现 > Map.Entry (getKey,getValue)
          //向下转型 Map.Entry
          Map.Entry m = (Map.Entry) entry;
            System.out.print(m.getValue()+" ");
        }
    }
}