InvoiceIdServer.java

package com.company;

import java.io.*;
public class InvoiceIdServer implements Serializable {
    private  int idCounter;
    private static InvoiceIdServer server;
    private InvoiceIdServer() {
        idCounter = 10001;
    }
    public static InvoiceIdServer instance() {
        if (server == null) {
            return (server = new InvoiceIdServer());
        } else {
            return server;
        }
    }
    public int getId() {
        return idCounter++;
    }
    public String toString() {
        return ("IdServer" + idCounter);
    }
    public static void retrieve(ObjectInputStream input) {
        try {
            server = (InvoiceIdServer) input.readObject();
        } catch(IOException ioe) {
            ioe.printStackTrace();
        } catch(Exception cnfe) {
            cnfe.printStackTrace();
        }
    }
    private void writeObject(java.io.ObjectOutputStream output) throws IOException {
        try {
            output.defaultWriteObject();
            output.writeObject(server);
        } catch(IOException ioe) {
            ioe.printStackTrace();
        }
    }
    private void readObject(java.io.ObjectInputStream input) throws IOException, ClassNotFoundException {
        try {
            input.defaultReadObject();
            if (server == null) {
                server = (InvoiceIdServer) input.readObject();
            } else {
                input.readObject();
            }
        } catch(IOException ioe) {
            ioe.printStackTrace();
        }
    }
}