摆动输出在第一次运行时不会出现

Question

I am trying to perform a simple client server communication using swing in netbeans.First time when I run, it shows a blank window. I again run it without closing the first output window, it shows the desired output. I am attaching the code.

Thanks

import java.io.*;
import java.net.*;

public class serverg extends javax.swing.JFrame {

ServerSocket ss;
Socket s;
BufferedReader in;
PrintWriter out;

public serverg() {
    initComponents();       
}

 void work() {
    try {

        String line;
        ss = new ServerSocket(3500);
        s=new Socket();
        jTextArea1.append("waiting for connection");
        s=ss.accept();
        in = new BufferedReader(new InputStreamReader(s.getInputStream()));
        out = new PrintWriter(s.getOutputStream());
        out.print("connection established");
        if((line=in.readLine())!=null)
        jTextArea1.append("Client : " + line );

    } catch (IOException r) {
    }

}

@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jScrollPane1 = new javax.swing.JScrollPane();
    jTextArea1 = new javax.swing.JTextArea();
    jTextField1 = new javax.swing.JTextField();
    jButton1 = new javax.swing.JButton();
    jLabel1 = new javax.swing.JLabel();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setName("Form"); // NOI18N

    jScrollPane1.setName("jScrollPane1"); // NOI18N

    /*try{
        jTextArea1.setEditable(false);
        //s=new Socket();
        jTextArea1.append("waiting for client..." );
        s=ss.accept();
        String line=in.readLine();
        jTextArea1.append("Client : " + line );
    }
    catch(IOException r){}*/
    jTextArea1.setColumns(20);
    jTextArea1.setRows(5);
    jTextArea1.setName("jTextArea1"); // NOI18N
    jScrollPane1.setViewportView(jTextArea1);

    jTextField1.setName("jTextField1"); // NOI18N

    org.jdesktop.application.ResourceMap resourceMap = org.jdesktop.application.Application.getInstance(desktopapplication1.DesktopApplication1.class).getContext().getResourceMap(serverg.class);
    jButton1.setText(resourceMap.getString("jButton1.text")); // NOI18N
    jButton1.setName("jButton1"); // NOI18N
    jButton1.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jButton1ActionPerformed(evt);
        }
    });

    jLabel1.setName("jLabel1"); // NOI18N

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jTextField1, javax.swing.GroupLayout.DEFAULT_SIZE, 380, Short.MAX_VALUE)
                .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 380, Short.MAX_VALUE)
                .addGroup(layout.createSequentialGroup()
                    .addGap(10, 10, 10)
                    .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 43, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addGap(98, 98, 98)
                    .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 68, javax.swing.GroupLayout.PREFERRED_SIZE)))
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 187, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 51, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 19, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 30, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addContainerGap())
    );

    pack();
}// </editor-fold>                        

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    String line = jTextField1.getText();
    out.println(line);
    jTextArea1.append("\nServer : " + line);
}                                        

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {

    java.awt.EventQueue.invokeLater(new Runnable() {

        public void run() {
            serverg ob=new serverg();                
            ob.setVisible(true);                      
            ob. jTextArea1.append("waiting for connection"  );
            ob.work();              
        }
    });

}
// Variables declaration - do not modify                     
private javax.swing.JButton jButton1;
private javax.swing.JLabel jLabel1;
private javax.swing.JScrollPane jScrollPane1;
private static javax.swing.JTextArea jTextArea1;
private javax.swing.JTextField jTextField1;
// End of variables declaration                   
}

Answer 1

Your work() method is not a part of your Swing Application , hence your main() method is wrong, simply change your work() method to this, so that both the processes can run on their respective threads, by writing s=ss.accept(); , you blocked your Event Dispatcher Thread.

Moreover, what ever changes you wanted to make to the GUI must be done on the Event Dispatcher Thread, so you need to change your work() method likewise, see Concurrency in Swing for more information. So revert your main method to this way, to sort things out.

public static void main(String args[]) 
{
    final serverg ob=new serverg();  
    java.awt.EventQueue.invokeLater(new Runnable() 
    {
        public void run() 
        {                         
            ob.setVisible(true);                      
            ob. jTextArea1.append("waiting for connection"  );                        
        }       
    });
    ob.work(); 
}

Your if block inside work() method , must look like this, for this to work, you must declare your line variable as Instance Variable :

if((line=in.readLine())!=null)
    SwingUtilities.invokeLater(new Runnable()
    {
        public void run()
        {
            jTextArea1.append("Client : " + line );
        }
    });