how to connect forms in java swing? [closed]

this is code

public class ServerskiOdgovor implements Serializable{
    private Object odgovor;
    private String poruka;

    public ServerskiOdgovor() {
    }

    public ServerskiOdgovor(Object odgovor, String poruka) {
        this.odgovor = odgovor;
        this.poruka = poruka;
    }

    public String getPoruka() {
        return poruka;
    }

    public void setPoruka(String poruka) {
        this.poruka = poruka;
    }

    public Object getOdgovor() {
        return odgovor;
    }

    public void setOdgovor(Object odgovor) {
        this.odgovor = odgovor;
    }



}
public class KlijentskiZahtev implements Serializable{
    private int  operacija;
    private Object parametar;
    private Object parametar2;


    public KlijentskiZahtev() {
    }

    public KlijentskiZahtev(int operacija, Object parametar, Object parametar2) {
        this.operacija = operacija;
        this.parametar = parametar;
        this.parametar2 = parametar2;
    }

    public Object getParametar2() {
        return parametar2;
    }

    public void setParametar2(Object parametar2) {
        this.parametar2 = parametar2;
    }

    public Object getParametar() {
        return parametar;
    }

    public void setParametar(Object parametar) {
        this.parametar = parametar;
    }

    public int getOperacija() {
        return operacija;
    }

    public void setOperacija(int operacija) {
        this.operacija = operacija;
    }
}
//server
public class ServerskaNit extends Thread {

    @Override
    public void run() {
        try {
            ServerSocket ss = new ServerSocket(9000);
            while (true) {
                Socket s = ss.accept();

                ObradaZahteva oz = new ObradaZahteva(s);
                oz.start();
            }

        } catch (IOException ex) {
            Logger.getLogger(ServerskaNit.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

public class ObradaZahteva extends Thread {


    Socket s;


    public ObradaZahteva(Socket s) {
        this.s = s;
    }



    @Override
    public void run() {

        while (true) {
            KlijentskiZahtev kz = primiZahtev();
            ServerskiOdgovor so = new ServerskiOdgovor();
            switch (kz.getOperacija()) {
                case 1:
                    break;
            }
            posaljiOdgovor(so);
        }

    }

    private KlijentskiZahtev primiZahtev() {
        KlijentskiZahtev kz = new KlijentskiZahtev();
        try {
            ObjectInputStream ois = new ObjectInputStream(s.getInputStream());
            kz = (KlijentskiZahtev) ois.readObject();
        } catch (IOException ex) {
            Logger.getLogger(ObradaZahteva.class.getName()).log(Level.SEVERE, null, ex);
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(ObradaZahteva.class.getName()).log(Level.SEVERE, null, ex);
        }
        return kz;
    }

    private void posaljiOdgovor(ServerskiOdgovor so) {
        try {
            ObjectOutputStream oos = new ObjectOutputStream(s.getOutputStream());
            oos.writeObject(so);
        } catch (IOException ex) {
            Logger.getLogger(ObradaZahteva.class.getName()).log(Level.SEVERE, null, ex);
        }

    }

}
public class ConnectionFactory {

    private Connection connection;
    public static ConnectionFactory instance;

    private ConnectionFactory() throws SQLException {
        String url="jdbc:mysql://localhost:3306/prosoftjul19";
        String username="root";
        String password="";
        try {
            connection = DriverManager.getConnection(url,username,password);
            connection.setAutoCommit(false);
        } catch (SQLException ex) {
            throw new SQLException("Connection is not created!");
        }
    }


    public Connection getConnection() {
        return connection;
    }
    public static ConnectionFactory getInstance() throws SQLException{
        if(instance == null){
            instance= new ConnectionFactory();
        }
        return instance;
    }
}
public class Kontroler {

    DBBroker broker;
    private static Kontroler instance;

    private Kontroler() {
        broker = new DBBroker();
    }

    public static Kontroler getInstance() {
        if (instance == null) {
            instance = new Kontroler();
        }
        return instance;
    }
    }
//klijent
public class KomunikacijaSaServerom {
    Socket s;
    private static KomunikacijaSaServerom instance;
    private KomunikacijaSaServerom() {
        try {
            s=new Socket("localhost", 9000);
        } catch (IOException ex) {
            Logger.getLogger(KomunikacijaSaServerom.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public static KomunikacijaSaServerom getInstance() {
        if(instance==null){
            instance=new KomunikacijaSaServerom();
        }
        return instance;
    }
    public ServerskiOdgovor primiOdgovor(){
        ServerskiOdgovor so=new ServerskiOdgovor();
        try {
            ObjectInputStream ois=new ObjectInputStream(s.getInputStream());
            so=(ServerskiOdgovor) ois.readObject();
        } catch (IOException ex) {
            Logger.getLogger(KomunikacijaSaServerom.class.getName()).log(Level.SEVERE, null, ex);
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(KomunikacijaSaServerom.class.getName()).log(Level.SEVERE, null, ex);
        }
        return so;
    }

    public void posaljiZahtev(KlijentskiZahtev kz) {
        try {
            ObjectOutputStream oos=new ObjectOutputStream(s.getOutputStream());
            oos.writeObject(kz);
        } catch (IOException ex) {
            Logger.getLogger(KomunikacijaSaServerom.class.getName()).log(Level.SEVERE, null, ex);
        }

    }
}
```