Call virtual method in contractor.

program.cs

class Program
{
    static void Main(string[] args)
    {
        BaseClass bc = new ChlidClass();
        Console.ReadLine();
    }
}

public class BaseClass
{
    public BaseClass()
    {
        this.Do();
    }

    protected virtual void Do()
    {
    }
}

public class ChlidClass : BaseClass
{
    private string message = null;

    public ChlidClass()
    {
        message = "Hi";
    }

    protected override void Do()
    {
        if (message.Contains("Hi"))
        {
            Console.WriteLine(message);
        }
    }
}