Question

In Java, how I can get an open socket? I have 2 JFrames; in the first JFrame I open the connection of my Client socket. Inside this same JFrame I create an instance of another JFrame (JFrame2). Now I want to get the same Socket from JFrame1 into JFrame2 to continue talking with my server Socket:

login.java(First JFrame)

try {
            cliente = new Socket("localhost", 4444);
            salida = new ObjectOutputStream(cliente.getOutputStream());
            entrada = new ObjectInputStream(cliente.getInputStream());
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: localhost.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: localhost.");
            System.exit(1);
        }

login.java(First Jframe)

try {           

            while ((mensaje_entrada=(String)entrada.readObject()) != null) {
                try {
                    me=td.encrypt(mensaje_entrada);
                    m2=td.decrypt(me);
                } catch (Exception ex) {
                    Logger.getLogger(Login.class.getName()).log(Level.SEVERE, null, ex);
                }
                System.out.println("e:"+ me);
                System.out.println("de:"+ m2);

                System.out.println(mensaje_entrada);
                if(mensaje_entrada.equals("20")){
                    mensaje_salida=""+txt_usuario.getText()+","+txt_password.getText();
                    System.out.println(mensaje_salida);
                    salida.writeObject( mensaje_salida );
                    salida.flush();
                    mensaje_entrada=(String)entrada.readObject();
                    System.out.println(mensaje_entrada);
                    if(mensaje_entrada.equals("1")){
                        m.setLocationRelativeTo(null); <---- **m is another JFrame(Jframe2)**
                        m.setVisible(true);
                        //JOptionPane.showMessageDialog(this,"Funciona!!");
                        break;
                    }else if(mensaje_entrada.equals("2")){
                        JOptionPane.showMessageDialog(this,"Usuario o contraseña incorrecta!","Error!",JOptionPane.ERROR_MESSAGE);
                        break;
                    }
                }

            }

        } catch (EOFException ex) { //This exception will be caught when EOF is reached
            System.out.println("End of file reached.");    
        } catch (ClassNotFoundException ex) {
            JOptionPane.showMessageDialog(this,ex.getMessage());
        } catch (IOException ex) {
            JOptionPane.showMessageDialog(this,ex.getMessage());
        }

Answer 1

Please take a look at the implementation of Singleton

With this you can access your object in an elegant way from everywhere and warranties that it will be uniquely instantiated.

A simple implementation following the approach of singleton for it:

package foo.bar;

import java.io.IOException;
import java.net.Socket;

public final class MySingletonSocket extends Socket {

    private static Socket clientSocket;

    static {
        try {
            clientSocket = new MySingletonSocket("localhost", 4444);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private MySingletonSocket(final String address, final int port) throws IOException {
        super(address, port);
    }

    public static final Socket getInstance() {
        return clientSocket;
    }

}

From JFrame1 you can access it like:

MySingletonSocket.getInstance()

From JFrame2 you can access it in the same way.