Invocation order of base classes and subclasses (C#,java)

Now the idea of OO programming has become more and more accepted, but we are not familiar with some basic things, such as the order of invocation of base classes and subclasses. Here I take C # as an example for you to explain
For a section of code below
public class BaseClass
{
public string a= "BaseClass";
Public BaseClass ()
{
A= "Initialization of BaseClass";
}

}
public class Extendclass:baseclass
{
private string b= "Extendclass";
Public Extendclass (): Base ()
{
b= "Initialization of Extendclass";

}

}
If we write code like this,
BaseClass a=new Extendclass ()
Procedure execution procedure execution steps
1. private string b= "Extendclass";
2. public string a= "BaseClass";
3. Public BaseClass ()
{
A= "Initialization of BaseClass";
}
4.public Extendclass (): Base ()
{
b= "Initialization of Extendclass";

}
This is the example I explained in C #, of course, other languages can be performed in different processes, as I know, the Java implementation process and C # is not only the same.
The process of his execution was
1. public string a= "BaseClass";
2. private string b= "Extendclass";
3. Public BaseClass ()
{
A= "Initialization of BaseClass";
}
4.public Extendclass (): Base ()
{
b= "Initialization of Extendclass";

}

VB.net is

1. public string a= "BaseClass";
2. Public BaseClass ()
{
A= "Initialization of BaseClass";
}

3. Private string b= "Extendclass";

4.public Extendclass (): Base ()
{
b= "Initialization of Extendclass";

}
All right, just write it here and do a good job.