// 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;

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),

// Use the ToString method defined in WorkItem.

// 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.

// Keep the console open in debug mode.
Console.WriteLine("Press any key to exit.");
/* Output:
1 - Fix Bugs
2 - Change the Design of the Base Class