Sealed Classes

Sealed Classes

Sealed class is the opposite of abstract class. When abstract class can not be instantiated as stand-alone class object, sealed class can only be instantiated as stand-alone object. It can not be used as a base class.

Any attempt to use it as the base class of another class will produce a compile error. See following code sample:

public sealed class mySealedClass
{
 public int myField;
 public void myMethod()
 {
  Console.WriteLine("This is my Sealed class");
 }
}

public class inherritedClass : mySealedClass    //compile error
{
 ....
}

Static Classes

A static class is a class where all the members are static. Static classes are used to group data and functions that are not affected by instance data. A common use of a static class might be to create a math library containing sets of mathematical methods and values.

The important things to know about a static class are the following:

• The class itself must be marked static.
• All the members of the class must be static.
• The class can have a static constructor, but it cannot have an instance constructor, since you cannot create an instance of the class.
• Static classes are implicitly sealed. That is, you cannot inherit from a static class.

The following code shows an example of a static class:

static public class MyMath  //static class, all members should be static
{
 public static float PI = 3.14f;
 public static bool IsOdd(int x)
 { 
  return x % 2 == 1; 
 }
 
 public static int square(int x)
 { 
  return x * x; 
 }
}

class Program
{
 static void Main( )
 { 
  int val = 3;
  Console.WriteLine(val + " is odd is " + MyMath.IsOdd(val));
  Console.WriteLine("square(" + val + ") = " + MyMath.square(val));
 }
}

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