Question

Which class design is better and why?

public class User {     public String UserName;     public String Password;     public String FirstName;     public String LastName; }  public class Employee : User {     public String EmployeeId;     public String EmployeeCode;     public String DepartmentId; }  public class Member : User {     public String MemberId;     public String JoinDate;     public String ExpiryDate; } 

OR

public class User {     public String UserId;     public String UserName;     public String Password;     public String FirstName;     public String LastName; }  public class Employee {     public User UserInfo;     public String EmployeeId;     public String EmployeeCode;     public String DepartmentId; }  public class Member {     public User UserInfo;     public String MemberId;     public String JoinDate;     public String ExpiryDate; } 

Answer 1

The question is simply answered by recognising that inheritance models an ‘IS-A’ relationship, while membership models a ‘HAS-A’ relationship.

• An employee IS A user
• An employee HAS A userinfo

Which one is correct? This is your answer.