ProductList.java

import java.util.*;
// import java.lang.*;
import java.io.*;
public class ProductList implements Serializable {
    private static final long serialVersionUID = 1L;
    private List<Product> products = new LinkedList<Product>();
    private static ProductList productlist;
    private ProductList() {
    }
    public static ProductList instance() {
      if (productlist == null) {
        return (productlist = new ProductList());
      } else {
        return productlist;
      }
    }
    
    public boolean insertProduct(Product product) {
      products.add(product);
      return true;
    }

    public Iterator<Product> getProducts() {
      return products.iterator();
    }

    private void writeObject(java.io.ObjectOutputStream output) {
      try {
        output.defaultWriteObject();
        output.writeObject(productlist);
      } catch(IOException ioe) {
        System.out.println(ioe);
      }
    }

    private void readObject(java.io.ObjectInputStream input) {
      try {
        if (productlist != null) {
          return;
        } else {
          input.defaultReadObject();
          if (productlist == null) {
              productlist = (ProductList) input.readObject();
          } else {
            input.readObject();
          }
        }
      } catch(IOException ioe) {
        System.out.println("in Catalog readObject \n" + ioe);
      } catch(ClassNotFoundException cnfe) {
        cnfe.printStackTrace();
      }
    }
    
    public String toString() {
      return products.toString();
    }
}