Client-server application null pointer exception_问答_开发者

I am working on a mini-project which consists of doing a client-server chat application. The application has a GUI and my problem is that I am trying to get the information from GUI and connect on that server, but I receive a null pointer exception. So far I have this code for the client(the server was tested without GUI client and works perfectly).

The GUI class:

package tema09client;
public class GUI extends javax.swing.JFrame {
    Comunicare test;
    String host, port, uname;
    int init=0;

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

        jPanel1 = new javax.swing.JPanel();
        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        jTextField1 = new javax.swing.JTextField();
        jLabel3 = new javax.swing.JLabel();
        jTextField2 = new javax.swing.JTextField();
        jLabel4 = new javax.swing.JLabel();
        jTextField3 = new javax.swing.JTextField();
        jButton1 = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Network chat");
        setBackground(new java.awt.Color(255, 255, 255));
        setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR));

        jPanel1.setBackground(new java.awt.Color(255, 255, 255));

        jLabel1.setText("Pentru a va loga selectati host-ul si portul, apoi scrieti-va username-ul in causta si apasati OK.");

        jLabel2.setText("HOST");

        jTextField1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jTextField1ActionPerformed(evt);
            }
        });

        jLabel3.setText("PORT");

        jLabel4.setText("USERNAME");

        jButton1.setText("Connect");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addGap(79, 79, 79)
                        .addComponent(jLabel1))
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addGap(55, 55, 55)
                        .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addGroup(jPanel1Layout.createSequentialGroup()
                                .addComponent(jLabel3)
                                .addGap(18, 18, 18)
                                .addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, 57, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(132, 132, 132)
                                .addComponent(jButton1))
                            .addGroup(jPanel1Layout.createSequentialGroup()
                                .addComponent(jLabel2)
                                .addGap(18, 18, 18)
                                .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 114, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(84, 84, 84)
                                .addComponent(jLabel4, javax.swing.GroupLayout.PREFERRED_SIZE, 72, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                                .addComponent(jTextField3, javax.swing.GroupLayout.DEFAULT_SIZE, 155, Short.MAX_VALUE)))))
                .addGap(81, 81, 81))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 23, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(37, 37, 37)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, 22, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jLabel4, javax.swing.GroupLayout.PREFERRED_SIZE, 18, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jTextField3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel3, javax.swing.GroupLayout.PREFERRED_SIZE, 22, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jButton1))
                .addContainerGap(185, Short.MAX_VALUE))
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

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

    private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {                                            

    }                                           

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        try{
        if(init==0){
                host=jTextField1.getText();
                port=jTextField2.getText();
                System.out.println(host+" "+port);
                if((host!=null) && (port!=null)){
                    test=new Comunicare(host, Integer.getInteger(port));
                    test.start();
                    init=1;
                }
            }

        test.setMesaj("cheieloginStep1");
        uname=jTextField3.getText();
        test.setUname(uname);
        }catch (NullPointerException e) {
                System.out.println(e);
            }
    }                                        


    // Variables declaration - do not modify                     
    private javax.swing.JButton jButton1;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel jLabel3;
    private javax.swing.JLabel jLabel4;
    private javax.swing.JPanel jPanel1;
    private javax.swing.JTextField jTextField1;
    private javax.swing.JTextField jTextField2;
    private javax.swing.JTextField jTextField3;
    // End of variables declaration                   

    public String getHost(){
        return jTextField1.getText();
    }

    public String getPort(){
        return jTextField2.getText();
    }

    public String getUsername(){
        return jTextField2.getText();
    }
}

The thread which connects to host:

package tema09client;

import java.net.*;
import java.io.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Comunicare extends Thread{
    Socket client=null;
    PrintWriter out=null;
    BufferedReader in=null;
    boolean listen=true;
    String username=null;
    String mesaj=null;

    public Comunicare(String host, int port){
        try {
            client = new Socket(host, port);
            out=new PrintWriter(client.getOutputStream());
            in=new BufferedReader(new InputStreamReader(client.getInputStream()));
            //out.println("loginStep1");
        } catch (UnknownHostException ex) {
            Logger.getLogger(Comunicare.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(Comunicare.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    @Override
    public void run(){
        String buffer;
        String line;
        while(listen){
            try {
                out.flush();
                buffer = in.readLine();
                if(buffer.startsWith("cheie")){
                    System.out.println("Serverul a trimis: "+buffer);
                    if(buffer.equals("cheieOKStep1")){
                        out.println("cheieloginStep2");
                        System.out.println("Am trimis: loginStep2");
                        out.flush();
                        logare();
                    //out.flush();
                    }
                    if(buffer.equals("cheieLoggedIn")){
                    System.out.println("Conectat! ... se incarca lista de prieteni online.");
                    }
                    if(buffer.equals("cheieFail"))
                        System.out.println("Username-ul nu este in baza de date.");
                    if(buffer.equals("cheieActualizarePrieteni"))
                        System.out.println("Acum se adauga prietenii in lista");
                }
                if(mesaj.startsWith("cheie")){
                    if(mesaj.equals("cheieloginStep1"))
                        out.println(mesaj);
                }
            } catch (IOException ex) {
                System.out.println(ex);
            }
        }
    }

    private void logare(){
        out.println(username);
        System.out.println("Am trimis: "+username);
    }

    public void setUname(String user){
        username=user;
    }

    public void setMesaj(String mesaj){
        this.mesaj=mesaj;
    }
}

And the main:

package tema09client;
public class Main {
    public static void main(String[] args) {
        GUI fereastra=new GUI();
        fereastra.setVisible(true);
    }

}

I think this is the stack trace:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
at tema09client.GUI.jButton1ActionPerformed(GUI.java:124) 
at tema09client.GUI.access$100(GUI.java:2) 
at tema09client.GUI$2.actionPerformed(GUI.java:48) 
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995) 
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)

ETC. This is line 124 from GUI: test=new Comunicare(host, Integer.getInteger(port));

Can anyone help me please? PS: The null pointer exception fires when I press "Connect" button.开发者_高级运维

Use Integer.parseInt(port) and not Integer.getInteger(port). Integer.getInteger(port) is used to get integer from the system property specified by port, and since it returns null and you need to unbox the Integer to int, you get NPE.

Moreover, you might get NPE in many places in your code, since you don't check for null values almost nowhere. you use out, in, socket and buffer without checking if null.