Thread: null pointer exception on extending a server class

Hey everyone, I am getting a null pointer exception (I will highlight the location after the code is shown). I am trying to extend a class that is a server:

 
import java.io.IOException;
import java.io.*;
import java.net.*;
public class MultiChatServer extends MultiEchoServer{
 
	static private ServerSocket serverSocket;
	 static private Socket connection;
 
	//serversocket instanciation
	public MultiChatServer(int port) throws IOException{
		super(port);
		//create a list to store all the the connections
	}
 
	public static void main(String args[])throws IOException{
 
		new MultiChatServer(4433);//construct a serversocket
 
		while(true){
			//STEP2: Do a blocking listen to the established server socket
			//when a new connection occurs, the accept method will trigger and and another thread will be instantiated
			connection = serverSocket.accept(); 
			System.out.println("New client requesting to connect on connection "+ (connection.getInetAddress().getHostName()));
			HandlerThread newThread = new HandlerThread(connection); //pass connection to be threaded
			System.out.println("Started a new thread for new client");
			newThread.start(); //envokes run method	
		}
		//serverSocket.close();
 
 
	}
 
 
}

The line

connection = serverSocket.accept();

causes the nullPointerException.

Just to be complete, here is the class i am extending:

import java.io.*;
import java.net.*;
 
public class MultiEchoServer{	
//Initialise variables
		static private ServerSocket serverSocket = null;
		static private Socket connection = null;
 
	//constructor
	public MultiEchoServer(int port) throws IOException{
		try{
			System.out.println("Server waiting for a client to connect on port 4433" );
			serverSocket = new ServerSocket(port);
		}catch(IOException e){
			System.err.println("Could not listen on port: 4433");
			System.exit(1);
		}
	} //end constructor
 
 
	public static void main(String args[])throws IOException{
 
		new MultiEchoServer(4433);
 
		while(true){
 
			connection = serverSocket.accept(); 
			System.out.println("New client requesting to connect on connection "+ (connection.getInetAddress().getHostName()));
			HandlerThread newThread = new HandlerThread(connection); 
			System.out.println("Started a new thread for new client");
			newThread.start(); 
		}
		//serverSocket.close();
 
	}
}

All I am trying to do is be in a position to have the same functionality as the superclass. I want to redefine the while loop in the main in the subclass.

When I extend MultiEchoServer, am I correct to say that the main method is not inherited? I thought that when I extend a superclass then I only get the functionality of the previous constructor.

If this is not the case, how do I modify the main? What I want to do is add extra line of code in the main of the subclass.