@Test
    public void LinkedHashMap() {

        Map<String, String> map = new LinkedHashMap<>();
        map.put("1key", "1value");
        map.put("2key", "2value");
        map.put("3key", "3value");
        Iterator it = map.entrySet().iterator();
        System.out.println("依照加入顺序打印map");
        while (it.hasNext()) {
            Map.Entry entity = (Map.Entry) it.next();
            System.out.println(entity);
        }
    }