ClientList.java

package com.company;
import java.util.*;
import java.io.*;
public class ClientList implements Serializable {
    private static final long serialVersionUID = 1L;
    private List<Client> clients = new LinkedList<Client>();
    private static ClientList clientList;
    private WaitlistList waitlists = new WaitlistList();
    ProductList productList = ProductList.instance();
    private ClientList() { }
    public static ClientList instance() {
        if (clientList == null) {
            return (clientList = new ClientList());
        } else {
            return clientList;
        }
    }

    public boolean insertMember(Client client) {
        clients.add(client);
        return true;
    }

    public Iterator<Client> getClients(){
        return clients.iterator();
    }

    private void writeObject(java.io.ObjectOutputStream output) {
        try {
            output.defaultWriteObject();
            output.writeObject(clientList);
        } catch(IOException ioe) {
            ioe.printStackTrace();
        }
    }
    private void readObject(java.io.ObjectInputStream input) {
        try {
            if (clientList != null) {
                return;
            } else {
                input.defaultReadObject();
                if (clientList == null) {
                    clientList = (ClientList) input.readObject();
                } else {
                    input.readObject();
                }
            }
        } catch(IOException ioe) {
            ioe.printStackTrace();
        } catch(ClassNotFoundException cnfe) {
            cnfe.printStackTrace();
        }
    }
    public String toString() {
        return clients.toString();
    }

    public void GenerateOrder(Client client)
    {
        for (int i = 0; i < client.userCart.shoppingCart.size(); i++)
        {
            Product cartP = client.userCart.shoppingCart.get(i);
            int pos = productList.IDcheck(cartP.getId());
            Product baseP = productList.get_listed_obj(pos) ;
            if(baseP.getQuantity() < cartP.getQuantity())
            {
                waitlists.AddWaitList(client,cartP,cartP.getQuantity());
            }
        }
        client.newInvoice();
    }

    public void PrintWaitList(Client client)
    {
        waitlists.PrintWaitList(client);
    }

    public int IDcheck (int ID) {
        for (int i=0; i < clients.size(); i++) {
            Client temp = clients.get(i);
            if (ID == temp.getId()) {
                System.out.println("ID found");
                return i;
            }
        }
        System.out.println("ERROR: ID is not in database");
        return -1;
    }
    public Client get_listed_obj (int position) {
        return clients.get(position);
    }
    public void set_listed_obj (int position, Client update) {
        clients.set(position, update);
    }
}