What is the meaning of “: base” in the constructor definition?

Question

What is the meaning of " : base " in the costructor of following class(MyClass) ? Please explain the concept behind constructor definition given below for class MyClass.

public class MyClass: WorkerThread
{
        public MyClass(object data): base(data) 
        { 
           // some code       

        }
}

public abstract class WorkerThread
{

        private object ThreadData;
        private Thread thisThread;

        public WorkerThread(object data)
        {
            this.ThreadData = data;
        }

        public WorkerThread()
        {
            ThreadData = null;
        }
}

Answer 1

The base class is WorkerThread. When you create a MyClass, a WorkerThread must be created, using any of its constructors.

By writing base(data) you are instructing the program to use one WorkerThread's constructor which takes data as a parameter. If you didn't do this, the program would try to use a default constructor - one which can be called with no parameters.

Answer 2

It calls the constructor of the class it inherits from, and provides the according arguments.

Sort of like calling

new WorkerThread(data)

Answer 3

It means you are passing the data parameter passed to the MyClass constructor through to the constructor of the base class (WorkerThread) in effect calling

public WorkerThread(object data)
{
    this.ThreadData = data;
}

Answer 4

A rare case where VB may be clearer...

Public Class MyClass
  Inherits WorkerThread

  Public Sub New(data)
    MyBase.New(data)
  End Sub

End Class