Let's talk OOP Again

Let’s talk OOP again

You will encounter same problem, no matter what kind of software products you design or develop:

how to design “User Object”?

I usually design “User Object” like this ( The following is a simple example):

I think most of us design “User Object” like this.

En , looked as if there is no problems , Moreover ,it had became some people's habit

We do like design “Add method” like “Add(xxx,xxx,xxx,xxx,xxx,xxx)”

But, when I review some base OOP knowledge recently; I found there is something wrong.

So, I change my old design(The following is sample example too):

 

If you can see I mind? Why “Example1” change to “Example2”?

Two important changes at there:

1, I use “Property” replace “public variable”;

public   virtual   string  UserName
         ... {
            get ...{ return _userName; }
            set
            ...{
                if (_userName != value)
                ...{
                    if (value.Length > 16||value.Length<4)
                    ...{
                        throw new Exception("you can input 4-16 characters to UserID only");
                    }
                    if(...)
                    ...{
                        throw new Exception("... ...")
                    }
                    if(...)
                    ...{
                        throw new Exception("... ...")
                    }
                    _userName = value;
                }
            }
        }

2, I use “Add (User xxx)” replace “Add (XXX,XXX,XXX)”;

Do you know why?

First, Use Property can get more control, the following code will show it:

You can code like this:

User objUser = new  User();
Users objUser = new  Users();
User.userName = TxtUserName.Text.Trim();
User.Password = TxtPassword.Text;
objUser.Add(objUser);

Attention, if username is too long or short, “User Object” will throw a Exception, we can catch this exception.

If you use old design,your code maybe like this:

User objUser = new  User();
String strUserName =  TxtUserName.Text.Trim();
String strPassword = TxtPassword.Text;
If(strUserName  > 16 ||  strUserName  < 4 )
... {
       … …
}
objUser.Add(strUserName,strPassword);

 

Which one more easy ?

 

Second, Like those method:”add”, “update” etc, use Object as parameter better than variable, It is more easy. You can see it from above code.

 

Third, it is most important thing: “Add”, "Update” methods not belong to “ User Object”, they should belong to “ Users Object” or belong to “ Dept Object”

 

I don’t know if you can understand the third. but you should try do it.

 

In this world, much thing we don’t know, but if when we try, we will get it