Java HashMap 放入数据时没有返回预期结果

Question

嗨，我想询问有关 java hashmap 的问题，这是我的代码

     HashMap<String, Object> hash_map = new HashMap<String, Object>(); 

        // Mapping string values to int keys 
        hash_map.put("SP", "A"); 
        hash_map.put("C1", "B"); 
        hash_map.put("C2", "C"); 

        //hash_map.put("C3", "You"); 

        // Displaying the HashMap 
        System.out.println("Initial Mappings are: " + hash_map); 

        // Inserting existing key along with new value 

        hash_map.put("C3", "D"); 
        hash_map.put("C4", "E"); 
        System.out.println("New map is: " + hash_map); 

这个结果

Initial Mappings are: {SP=A, C1=B, C2=C}

New map is: {C3=D, C4=E, SP=A, C1=B, C2=C}

我的预期结果

Initial Mappings are: {SP=A, C1=B, C2=C}

New map is: {SP=A, C1=B, C2=C, C3=D, C4=E}

Answer 1

一个HashMap按 hashCode 排序到存储桶中。要拥有保留插入顺序的 Map，请使用 LinkedHashMap 。就像，

Map<String, Object> hash_map = new LinkedHashMap<>();