what is differance between Action(T) and delegate?

When you use the Action delegate, you do not have to explicitly define a delegate that encapsulates a method with a single parameter.

using System;

using System.Windows.Forms;

delegate void DisplayMessage(string message);

public class TestCustomDelegate

{

public static void Main()

{

DisplayMessage messageTarget;

if (Environment.GetCommandLineArgs().Length > 1)

messageTarget = ShowWindowsMessage;

else

messageTarget = Console.WriteLine;

messageTarget("Hello, World!");

}

private static void ShowWindowsMessage(string message)

{

MessageBox.Show(message);

}