Map<String, String> map = new HashMap<>();

        map.put("key1", "value1");

        map.put("key2", "value2");

        map.put("key3", "value3");

        //通过Map.entrySet遍历key和value

        for (Map.Entry<String, String> entry : map.entrySet()) {

            System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());

        }

        //通过Map.keySet遍历key和value

        for (String key : map.keySet()) {

            System.out.println("key= "+ key + " and value= " + map.get(key));

        }

        //通过Map.values()遍历所有的value，但不能遍历key

        for (String v : map.values()) {

            System.out.println("value= " + v);

        }