Encapsulation in OOP

I am studying about OOP concepts. As I understood from the documents I have read, I wrote an example program for encapsulation concept in OOP. I pasted my code below. Is my concept about encapsulation is correct ?.

Default.aspx

<asp:Button ID="showBtn" Text="Show employee details." runat="server"/>

Default.aspx.cs

public partial class _Default : System.Web.UI.Page
{
Employee emp;

protected void Page_Load(object sender, EventArgs e)
{
    emp = new Employee();
    emp.SetEmployeeID(001);
    emp.SetEmployeeSalary(5000);
    emp.EmployeeName = "Rob";
    emp.EmployeeAge = 26;

    showBtn.Click += new EventHandler(showBtn_Click);
}

void showBtn_Click(object sender, EventArgs e)
{
    emp.ShowEmployeeDetails();
}
}

Class Employee

class Employee
{
private int empId;
private int empSalary;
private string empName;
private int empAge;

public void SetEmployeeID(int id)
{
    empId = id; //Mutator
}

public void SetEmployeeSalary(int sal)
{
    empSalary = sal;  //Mutator
}

public int GetEmployeeID()
{
    return empId;  //Accessor
}

public int GetEmployeeSalary()
{
    return empSalary;  //Accessor
}

public string EmployeeName
{
    get { return empName; }   //Accessor
    set { empName = value; }  //Mutator
}

public int EmployeeAge
{
    get { return empAge; }  //Accessor
    set { empAge = value; } //Mutator
}

private void ShowDetails()
{
    HttpContext.Current.Response.Write(this.GetEmployeeID() + " : " + this.EmployeeName + " : " + this.EmployeeAge + " : " + this.GetEmployeeSalary());
}

public void ShowEmployeeDetails()
{
    ShowDetails();
}
}

My main doubt is about the way I called the ShowDetails() method in the Employee. Is this a good way to hide the method ShowDetails() ?.

Solution

From an OO perspective, your ShowDetails method is doing two very different things.

Creating a string that represents the object
Outputting the string to the HttpResponse.

Now The first task does belong to the class Employee, you need to know what an employee is to be able to create a string that is representative of the object. In fact in .net this is such a common thing, there is in fact a "overridable" or "virtual" function called Object.ToString().

The second task has absolutely nothing to do with the class Employee, and A LOT to do with strings and HttpResponses (and in this case how we get the HttpResponse, which is to get it from the HttpContext, which means we MUST be on a webserver in a HttpRequest). With all these assumptions, it is extremely unsafe in an all purpose "data" or "domain" class.

This is how I would refactor this.

class Employee
{
    private int empId;
    private int empSalary;
    private string empName;
    private int empAge;

    public void SetEmployeeID(int id)
    {
        empId = id; //Mutator
    }

    public void SetEmployeeSalary(int sal)
    {
        empSalary = sal;  //Mutator
    }

    public int GetEmployeeID()
    {
        return empId;  //Accessor
    }

    public int GetEmployeeSalary()
    {
        return empSalary;  //Accessor
    }

    public string EmployeeName
    {
        get { return empName; }   //Accessor
        set { empName = value; }  //Mutator
    }

    public int EmployeeAge
    {
        get { return empAge; }  //Accessor
        set { empAge = value; } //Mutator
    }

    public override string ToString()
    {
        return this.GetEmployeeID() + " : " + 
            this.EmployeeName + " : " + 
            this.EmployeeAge + " : " + 
            this.GetEmployeeSalary();
    }


}

and

public partial class _Default : System.Web.UI.Page
{
    Employee emp;

    protected void Page_Load(object sender, EventArgs e)
    {
        emp = new Employee();
        emp.SetEmployeeID(001);
        emp.SetEmployeeSalary(5000);
        emp.EmployeeName = "Rob";
        emp.EmployeeAge = 26;

        showBtn.Click += new EventHandler(showBtn_Click);
    }

    void showBtn_Click(object sender, EventArgs e)
    {
        HttpContext.Current.Response.Write(emp.ToString());
    }
}

Since we KNOW for sure that there is a valid HttpContext.Current inside the webpage. Thus Employees don't need to know about the internet, and would equally be able to work on a WinForm application.