0

Consider the following class that just gets an IP and port number :

package view;


import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.net.InetAddress;
import javax.swing.*;
import javax.swing.border.EmptyBorder;


/**
 * Server side
 * @author X
 *
 */
class ServerConnector implements ActionListener
{

    private JFrame m_frame = null;
    private JTextField m_serverIP;
    private JTextField m_serverPort; // you can use also JPasswordField
    private JButton m_submitButton;

    // location of the jframe
    private final int m_centerX = 500;
    private final int m_centerY = 300;

    // dimensions of the jframe
    private final int m_sizeX = 1650;
    private final int m_sizeY = 150;

    private String m_ip;
    private String m_port;

    private boolean ready = false;

    /**
     * Ctor
     */
    ServerConnector()
    {
        m_frame = new JFrame("Sever Side Listener");
        m_frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        m_serverIP = new JTextField(20);
        m_serverPort = new JTextField(20);

        JPanel gui = new JPanel(new BorderLayout(3,3));
        gui.setBorder(new EmptyBorder(5,5,5,5));
        gui.setSize(m_sizeX , m_sizeY);
        m_frame.setContentPane(gui);

        JPanel labels = new JPanel(new GridLayout(0,1));
        JPanel controls = new JPanel(new GridLayout(0,1));
        gui.add(labels, BorderLayout.WEST);
        gui.add(controls, BorderLayout.CENTER);

        labels.add(new JLabel("Server IP: "));
        controls.add(m_serverIP);
        labels.add(new JLabel("Server Port: "));
        controls.add(m_serverPort);
        m_submitButton = new JButton("Start Listening");
        m_submitButton.addActionListener(this);

        gui.add(m_submitButton, BorderLayout.SOUTH);
        m_frame.setLocation(m_centerX , m_centerY);
        m_frame.setSize(m_sizeX , m_sizeY);
        m_frame.pack();
        m_frame.setVisible(true);
    }

    public static void main(String[] args) {
        new ServerConnector();
    }

    @Override
    public void actionPerformed(ActionEvent event) {

        Object object = event.getSource();
        if (object == this.m_submitButton)
        {
            // grab all values from the connection box 
            // if one of them is missing then display an alert message 

            String ip = this.m_serverIP.getText().trim();
            String port = this.m_serverPort.getText().trim();

            if (ip.length() == 0)
            {
                JOptionPane.showMessageDialog(null, "Please enter IP address !");
                return;
            }

            if (port.length() == 0)
            {
                JOptionPane.showMessageDialog(null, "Please enter Port number!");
                return;
            }

            int s_port = 0;

            try
            {
                // try parse the Port number 
                // throws exception when an incorrect IP address 
                // is entered , and caught in the catch block 
                s_port = Integer.parseInt(port);
            }

            catch(Exception exp)
            {
                JOptionPane.showMessageDialog(null, "Port number is incorrect!");
                return;
            }

            try
            {
                // try parse the IP address 
                // throws exception when an incorrect IP address 
                // is entered , and caught in the catch block 
                InetAddress.getByName(ip);
            }

            catch(Exception exp)
            {
                JOptionPane.showMessageDialog(null, "IP address is incorrect!");
                return;
            }

            m_frame.dispose();
            this.m_ip = ip;
            this.m_port = port;
            ready = true;
            // new ServerGUI(ip , s_port);
        }


    }


    public boolean isReady()
    {
        return this.ready;
    }

    /**
     * 
     * @return
     */
    public String[] getIPandPort()
    {
        String[] ipPort = new String[2];
        ipPort[0] = this.m_ip;
        ipPort[1] = this.m_port;
        return ipPort;
    }
}

And the would be controller class 

public class ServerController {

    String m_ip;
    int m_port;

    public static void main(String args[])
    {
        ServerConnector sc = new ServerConnector();

        while (!sc.isReady())
        {
            // run 
        }

        // get IP and port
        String[] ipPort = sc.getIPandPort();

        System.out.println("IP is :" + ipPort[0] + " and port is :" + ipPort[1]);

    }
}

For now ServerController is in a while(true) loop , until the user has entered the IP and Port.

How can I avoid this kind of dependency (avoid the while loop) ?

JAN
  • 21,236
  • 66
  • 181
  • 318

1 Answers1

2

First of all, get rid of the while (true) loop as its only purpose will be to mess your code up.

A general solution is to get the information from the user in code that blocks program flow. A problem occurs, though if this is needed in a GUI that cannot have its event thread blocked.

One Swing solution is as we have discussed previously in your previous question: use a modal dialog to get the information. The modality of the dialog will halt the program flow in the calling code until the dialog is handled.

If you want to avoid use of modal dialogs, then another general event-driven solution is to use a observer design pattern -- have one object be notified by another when information or state has changed. This can be achieved easily with use of PropertyChangeSupport and PropertyChangeListeners, although there are other ways as well, including using the XxxxListeners available in the Swing library.

For example of listener use and MVC with Swing:

Edit
For example, changes marked with a // !! comment:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.net.InetAddress;

import javax.swing.*;
import javax.swing.border.EmptyBorder;
import javax.swing.event.SwingPropertyChangeSupport;

public class ServerController {

   String m_ip;
   int m_port;
   private static String[] ipPort;

   public static void main(String args[]) {
      final ServerConnector sc = new ServerConnector();

      sc.addPropertyChangeListener(new PropertyChangeListener() {
         @Override
         public void propertyChange(PropertyChangeEvent evt) {
            if (ServerConnector.READY.equals(evt.getPropertyName())) {
               if (sc.isReady()) {
                  ipPort = sc.getIPandPort();
                  System.out.println("IP is :" + ipPort[0] + " and port is :" + ipPort[1]);
               }
            }
         }
      });
   }
}

class ServerConnector implements ActionListener {
   public static final String READY = "ready"; //!!

   private SwingPropertyChangeSupport pcSupport = new SwingPropertyChangeSupport(this); //!!
   private boolean ready = false;
   private JFrame m_frame = null;
   private JTextField m_serverIP;
   private JTextField m_serverPort; // you can use also JPasswordField
   private JButton m_submitButton;

   // location of the jframe
   private final int m_centerX = 500;
   private final int m_centerY = 300;

   // dimensions of the jframe
   private final int m_sizeX = 1650;
   private final int m_sizeY = 150;

   private String m_ip;
   private String m_port;


   /**
    * Ctor
    */
   ServerConnector() {
      m_frame = new JFrame("Sever Side Listener");
      m_frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      m_serverIP = new JTextField(20);
      m_serverPort = new JTextField(20);

      JPanel gui = new JPanel(new BorderLayout(3, 3));
      gui.setBorder(new EmptyBorder(5, 5, 5, 5));
      gui.setSize(m_sizeX, m_sizeY);
      m_frame.setContentPane(gui);

      JPanel labels = new JPanel(new GridLayout(0, 1));
      JPanel controls = new JPanel(new GridLayout(0, 1));
      gui.add(labels, BorderLayout.WEST);
      gui.add(controls, BorderLayout.CENTER);

      labels.add(new JLabel("Server IP: "));
      controls.add(m_serverIP);
      labels.add(new JLabel("Server Port: "));
      controls.add(m_serverPort);
      m_submitButton = new JButton("Start Listening");
      m_submitButton.addActionListener(this);

      gui.add(m_submitButton, BorderLayout.SOUTH);
      m_frame.setLocation(m_centerX, m_centerY);
      m_frame.setSize(m_sizeX, m_sizeY);
      m_frame.pack();
      m_frame.setVisible(true);
   }

   public static void main(String[] args) {
      new ServerConnector();
   }

   @Override
   public void actionPerformed(ActionEvent event) {

      Object object = event.getSource();
      if (object == this.m_submitButton) {
         // grab all values from the connection box
         // if one of them is missing then display an alert message

         String ip = this.m_serverIP.getText().trim();
         String port = this.m_serverPort.getText().trim();

         if (ip.length() == 0) {
            JOptionPane.showMessageDialog(null, "Please enter IP address !");
            return;
         }

         if (port.length() == 0) {
            JOptionPane.showMessageDialog(null, "Please enter Port number!");
            return;
         }

         int s_port = 0;

         try {
            // try parse the Port number
            // throws exception when an incorrect IP address
            // is entered , and caught in the catch block
            s_port = Integer.parseInt(port);
         }

         catch (Exception exp) {
            JOptionPane.showMessageDialog(null, "Port number is incorrect!");
            return;
         }

         try {
            // try parse the IP address
            // throws exception when an incorrect IP address
            // is entered , and caught in the catch block
            InetAddress.getByName(ip);
         }

         catch (Exception exp) {
            JOptionPane.showMessageDialog(null, "IP address is incorrect!");
            return;
         }

         m_frame.dispose();
         this.m_ip = ip;
         this.m_port = port;
         setReady(true); //!!
         // !! ready = true;
         // new ServerGUI(ip , s_port);
      }

   }

   // !! added
   public void setReady(boolean ready) {
      boolean oldValue = this.ready;
      boolean newValue = ready;
      this.ready = ready;
      pcSupport.firePropertyChange(READY, oldValue, newValue);
   }

   //!! added
   public void addPropertyChangeListener(PropertyChangeListener listener) {
      pcSupport.addPropertyChangeListener(listener);
   }

   //!! added
   public void removePropertyChangeListener(PropertyChangeListener listener) {
      pcSupport.removePropertyChangeListener(listener);
   }

   public boolean isReady() {
      return this.ready;
   }

   /**
    * 
    * @return
    */
   public String[] getIPandPort() {
      String[] ipPort = new String[2];
      ipPort[0] = this.m_ip;
      ipPort[1] = this.m_port;
      return ipPort;
   }
}
Community
  • 1
  • 1
Hovercraft Full Of Eels
  • 283,665
  • 25
  • 256
  • 373