// WorkItem implicitly inherits from the Object class.
public class WorkItem
{
// Static field currentID stores the job ID of the last WorkItem that
// has been created.
private static int currentID;
//Properties.
protected int ID { get; set; }
protected string Title { get; set; }
protected string Description { get; set; }
protected TimeSpan jobLength { get; set; }
// Default constructor. If a derived class does not invoke a base-
// class constructor explicitly, the default constructor is called
// implicitly. 
public WorkItem()
{
ID = 0;
Title = "Default title";
Description = "Default description.";
jobLength = new TimeSpan();
}
// Instance constructor that has three parameters.
public WorkItem(string title, string desc, TimeSpan joblen)
{
this.ID = GetNextID();
this.Title = title;
this.Description = desc;
this.jobLength = joblen;
}
// Static constructor to initialize the static member, currentID. This
// constructor is called one time, automatically, before any instance
// of WorkItem or ChangeRequest is created, or currentID is referenced.
static WorkItem()
{
currentID = 0;
}
protected int GetNextID()
{
// currentID is a static field. It is incremented each time a new
// instance of WorkItem is created.
return ++currentID;
}
// Method Update enables you to update the title and job length of an
// existing WorkItem object.
public void Update(string title, TimeSpan joblen)
{
this.Title = title;
this.jobLength = joblen;
}
// Virtual method override of the ToString method that is inherited
// from System.Object.
public override string ToString()
{
return String.Format("{0} - {1}", this.ID, this.Title);
}
}
// ChangeRequest derives from WorkItem and adds a property (originalItemID) 
// and two constructors.
public class ChangeRequest : WorkItem
{
protected int originalItemID { get; set; }
// Constructors. Because neither constructor calls a base-class 
// constructor explicitly, the default constructor in the base class
// is called implicitly. The base class must contain a default 
// constructor.
// Default constructor for the derived class.
public ChangeRequest() { }
// Instance constructor that has four parameters.
public ChangeRequest(string title, string desc, TimeSpan jobLen,
int originalID)
{
// The following properties and the GetNexID method are inherited 
// from WorkItem.
this.ID = GetNextID();
this.Title = title;
this.Description = desc;
this.jobLength = jobLen;
// Property originalItemId is a member of ChangeRequest, but not 
// of WorkItem.
this.originalItemID = originalID;
}
}
class Program
{
static void Main()
{
// Create an instance of WorkItem by using the constructor in the 
// base class that takes three arguments.
WorkItem item = new WorkItem("Fix Bugs",
"Fix all bugs in my code branch",
new TimeSpan(3, 4, 0, 0));
// Create an instance of ChangeRequest by using the constructor in
// the derived class that takes four arguments.
ChangeRequest change = new ChangeRequest("Change Base Class Design",
"Add members to the class",
new TimeSpan(4, 0, 0),
1);
// Use the ToString method defined in WorkItem.
Console.WriteLine(item.ToString());
// Use the inherited Update method to change the title of the 
// ChangeRequest object.
change.Update("Change the Design of the Base Class",
new TimeSpan(4, 0, 0));
// ChangeRequest inherits WorkItem's override of ToString.
Console.WriteLine(change.ToString());
// Keep the console open in debug mode.
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
/* Output:
    1 - Fix Bugs
    2 - Change the Design of the Base Class
*/