Java BufferedWriter when connected to server - null pointer exception - chat app

Question

It's a simple chat app. Server and client as separately app. Connection between server and client works fine. I have a problem when i'm trying to send String from Client by BufferedWriter to Server BufferedReader. I have null pointer exception.
And can you tell me that is everything fine with threads logic in this app ?

Server app

public class Server {
private int                 port    =   5000;
private ServerSocket        server  =   null;
private Socket              socket  =   null;
private InputStreamReader   isr     =   null;
private OutputStreamWriter  osw     =   null;
private BufferedReader      br      =   null;
private BufferedWriter      bw      =   null;
private Chat                chat;
private String              message;

private int                 bOffset =   10;
private JFrame              mainFrame;
private JPanel              mainPanel;
private JPanel              boxPanel;
private JLabel              boxTitleLabel;
private JTextArea           incomingMessagesJTextArea;
private JTextField          messageWritten;
private JButton             sendServerButton;

public static void main(String[] args){

    System.out.println("Server is running");
    new Server().createGUI();     //some swing GUI things
    new Server().createServerConnection();

}

public void createServerConnection(){

    try {

        /** Create socket for communication between apps */
        server = new ServerSocket(port);
        socket = server.accept();
        System.out.println("Server accept client: OK");

        /** Create output writers */
        osw = new OutputStreamWriter(socket.getOutputStream());
        bw = new BufferedWriter(osw);

        /** Create inputs readers */
        isr = new InputStreamReader(socket.getInputStream());   //data in bytes format
        br = new BufferedReader(isr);                           //data in character format

    } catch (IOException e) {
        System.out.println("Server Error createServerConnection(): " +e.getMessage());
    }

    /** Create new thread for read server-input data */
    new Thread(new Runnable() {
        public void run() {
            System.out.println("Server Thread - running");

            while (true) {

                try {
                        String message = br.readLine();
                        System.out.println(message);

                } catch (IOException e) {
                    System.out.println("Server Error createServerConnection() -> new Thread: " +e.getMessage());
                }
            }
        }
    }
    ).start();

}}

Client app

public class Client {
private int                 port    =   5000;
private Socket              socket  =   null;
private InputStreamReader   isr     =   null;
private OutputStreamWriter  osw     =   null;
private BufferedReader      br      =   null;
private BufferedWriter      bw      =   null;
private String              message;

private int                 bOffset =   10;
private JFrame              mainFrame;
private JPanel              mainPanel;
private JPanel              boxPanel;
private JLabel              boxTitleLabel;
private JTextArea           incomingMessagesJTextArea;
private JTextField          messageWritten;
private JButton             sendServerButton;

public static void main(String[] args){

    System.out.println("Client is running");
    new Client().createGUI();     //some swing GUI things
    new Client().createConnectionWithServer();
    new Client().sendTextToServer();
}

public void sendTextToServer(){

    try {
        message = "test";
        bw.write(message);  //null pointer exception
        bw.write('\n');
        bw.flush();

    } catch(Exception ex) {
        ex.printStackTrace();
    }
}

public void createConnectionWithServer(){

    try {

        /** Create socket for communication between apps */
        socket = new Socket("localhost", port);

        /** Create inputs readers */
        isr = new InputStreamReader(socket.getInputStream());   //data in bytes format
        br = new BufferedReader(isr);                           //data in characters format

        /** Create output writers */
        osw = new OutputStreamWriter(socket.getOutputStream());
        bw = new BufferedWriter(osw);

    } catch (IOException e) {
        System.out.println("Server Error createConnectionWithServer(): " +e.getMessage());
    }

    /** Create new thread for read client-input data */
    new Thread(new Runnable() {
        public void run() {
            System.out.println("Client Thread - running");

            while (true) {

                try {
                    message = br.readLine();
                    System.out.println(message);

                } catch (IOException e) {
                    System.out.println("Client Error createServerConnection() -> new Thread: " +e.getMessage());
                }
            }
        }
    }
    ).start();
}}

Answer 1

Change your main method to create a unique instance of your Client class:

    public static void main(String[] args){
        Client client = new Client();
        System.out.println("Client is running");
        client.createGUI();     //some swing GUI things
        client.createConnectionWithServer();
        client.sendTextToServer();
    }

You were creating a new instance of the Client class everytime you called the "new" statement. Doing so the variable were initialized in the fist instance, making impossible for the other one to acces the initialized variable (throwing NullPointerException)