Field output order when conver object to JSON

If we want to serialize the object into its equivalent JSON along with maintaining order of its attribute

we can make use of a map with key as string and value as an object (can use any as per the requirement )

Note:

Put the key value in reverse order and after the JSON.serialize() you will get the JSON in the desired format

Example: If we want the json for this class with attribute order maintained:

global class ResultDto {
    String ParlorCode;      // 1st
    String DepartmentCode;  // 2nd
    String EmployeeNumber;  // 3rd
    String Name;            // 4th
}

we can make use of map like below:

Map<String, Object> jsonObj = new Map<String, Object>();

// adding keys in reverse order
jsonObj.put('Name', 'some string text');
jsonObj.put('EmployeeNumber', 'some string text');
jsonObj.put('DepartmentCode', 'some string text');
jsonObj.put('ParlorCode', 'some string text');

String jsonOutput = JSON.serialize(jsonObj);

System.debug(jsonOutput);

Output:

{
    "ParlorCode": "some string text",
    "DepartmentCode": "some string text",
    "EmployeeNumber": "some string text",
    "Name": "some string text"
}

Actually this 'is' possible. Attributes are rendered in reverse order, so you can just rename them in reverse alphabetical order:

global class ResultDto {
    String zParlorCode;      // 1st
    String yDepartmentCode;  // 2nd
    String xEmployeeNumber;  // 3rd
    String wName;            // 4th
}

Of course explaining why your attributes are named like is is another question. As others have pointed out JSON should never depend on the order of the attributes being rendered. I have an edge scenario where a (dumb) report displays the first 200 characters of my Json field, and I'd like to therefore serialize the important data first.