C# Online Compiler | .NET Fiddle

using System;
					
public class Program
{
	public sealed class Student
	{
		// Stores the single instance if this class.
		private static Student oStudent;
		
		// Returns the single instance of this class.
		public static Student GetInstance()
		{
			if(oStudent == null)
			{
				oStudent = new Student();
			}
			
			return oStudent;
		}
		
		// Constructor declared private. 
		private Student()
		{
			//Initialization here
		}
		
		public void DisplayStudentInfo()
		{
			Console.WriteLine("Display Student info here.");
		}
		
		public void DisplayStudentName(string name)
		{
			Console.WriteLine(String.Format("Student name is {0}", name));
		}
		
		public class StudentDerivad : Student
	    {
		   //This class inherited Student class.
	    }
	}
	
	public static void Main()
	{
		// Create and get the single instance of class Student.
		Student oStudent1 = Student.GetInstance();
		oStudent1.DisplayStudentInfo();
		oStudent1.DisplayStudentName("Jhon");
		
		// Get the single instance of class Student
		Student oStudent2 = Student.GetInstance();
		oStudent2.DisplayStudentName("Jake");		
	}
}

 
using System;
                    
public class Program
{
    public sealed class Student
    {
        // Stores the single instance if this class.
        private static Student oStudent;
        
        // Returns the single instance of this class.
        public static Student GetInstance()
        {
            if(oStudent == null)
            {
                oStudent = new Student();
            }
            
            return oStudent;
        }
        
        // Constructor declared private. 
        private Student()
        {
            //Initialization here