create object object in java confusion

ProductCollection is a class. Typically in any OO language the program operates on instances of objects. Think of the class as a template for creating new instances of the class.

so the

pColl = new ProductCollection();

line creates a new ProductCollection instance and gives your a reference to that instance, pColl. On that particular line the type of pColl is not defined, so it must be somewhere else in the code before that line, or there is an error. You could do

ProductCollection pColl = new ProductCollection();

if that is the case. The next line

product extractedProduct;

means that extranctedProduct is a reference to an instance of product. As a note, if product is a class it should be Product with a capital P. Since you don't assign a value, extractedProduct is uninitialized.

import java.sql.*;
import java.net.*;
import java.io.*;
import java.util.Enumeration;

public class EServer
{

public static void main(String[] args)
{
   // Net and IO objects
   ServerSocket ss= null;
   Socket s = null;
   BufferedReader bf = null;
   PrintWriter pw = null;

   // Queries

   // Query which retireves all products
   String allQuery = "Select * from StoreProducts";
   // Query which retrieves products which are out of stock
   String outOfStockQuery = "Select * from StoreProducts where Quantity = 0";
   String queryString = "";
   String messageBack = "";

   // Database objects
   Connection cn = null;
   Statement query = null;
   ResultSet rs = null;

   String lineRead= "";
   ProductCollection pColl = new ProductCollection();
   Enumeration pEnumeration;

   try
   {
      // Server socket set up on port 2000
      ss = new ServerSocket(2000);

      System.out.println("...Server socket set up");
      // Set up a database
      Database db = new Database
        ("darrel", "", "sun.jdbc.odbc.JdbcOdbcDriver", "jdbc:odbc:", "products");
      System.out.println("...Database set up");
      // Get a connection to the database
      Database.establishConnection();
      cn = Database.getConnection();
      System.out.println("...Database connection set up");
      //Set up a query object
      query = cn.createStatement();
      // Loop waiting for connections
      int count = 1;
      while(true)
      {
         System.out.println("...Waiting for connection "+count);
         count++;
         s = ss.accept();
                 pw = new PrintWriter(s.getOutputStream(), true);
         bf = new BufferedReader(new InputStreamReader(s.getInputStream()));
                 boolean looper = true;
         while(true)
         {

             lineRead = bf.readLine();
             switch(lineRead.charAt(0))//
             {
                // Out of Stock command
                case 'O':{
                           queryString = outOfStockQuery;
                           break;
                         }
                // All products
                case 'A':{
                           queryString = allQuery;
                           break;
                         }
                // Client has terminated
                case 'E':{
                           looper = false;
                           break;
                          }
                 }
              //Check if client has terminated
              if(!looper) break;
              // Client has not terminated
              // Execute the required query and create result set
              rs = query.executeQuery(queryString);
              // Create collection of products
              pColl = new ProductCollection();
              // Process the rows that have been extracted
              // Place them in pColl
              Product extractedProduct;
              while(rs.next())
              {

*extractedProduct = (Product) pColl.addProduct(rs);*


              }
               // Form the collection of products, each terminated by asterisk
               pEnumeration = pColl.elements();
               // messageBack is to be concatenated to so initialise it to the empty string
               messageBack= "";
               while(pEnumeration.hasMoreElements())
               {
                  messageBack+=(Product)pEnumeration.nextElement()+"*";
               }
               // Now send back the collection string to the client for display
               pw.println(messageBack);
             }
          }
        }
        catch(Exception e)
           {System.out.println("Trouble setting up the database "+e);}
        // Close database connection
        try
        {
           cn.close();
        }
        catch(Exception e)
            {System.out.println("Problem closing connection");}
    }
}