只有一个 String 字段的模型类

Question

i have a class, which i would like refactor looks like this:

class PersonId {
    String personId
    //getter, setter
}

class Person{

   PersonId personId;
   //other fields...
}

It seems for me, that a class PersonId is unnecessary cause it contains only one string-field with a id-value. Actually this string-field could be placed directly into class Person. Is there a basic rule for class-design, that would allow a class 'PersonId'? Which disadvantage has a class 'PersionId' ?

Answer 1

As far as I know, if your class PersonId ONLY contains this String, then you can place it directly inside your Person class. On the other hand, if your class contains more than that (method or more attributes) then it is usefull.

Then only advantage I could see is that you can give the same PersonId to multiple Person, and if you modifie one, then it modifies the others :

Person p1 = new Person();
Person p2 = new Person();
PersonId id = new PersonId();
id.id = "abc";
p1.id = id;
p2.id = id;
System.out.println(p1.id.id); // abc (for p1 & p2)
id.id = "foo";
System.out.println(p1.id.id); // foo (for p1 & p2)
id.id = "ba";
System.out.println(p2.id.id); // ba (for p1 & p2)