We Keep Coding

How does the client wait for a server response

I have a simple server to client program that lets the server send text to the clients, There is no connection problems. However, I'm not sure what to put the while loop which updates the JLabel of the sent text. If I put while(true) I get an error saying no lines found.
import java.io.IOException;
import java.net.Socket;
import java.util.Scanner;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class Client {
private static JLabel l = new JLabel();
public Client() {
JFrame f = new JFrame("Client");
JPanel p = new JPanel(null);
f.setSize(300, 150);
f.setLocationRelativeTo(null);
l.setSize(300, 20);
l.setLocation(0, 65);
p.add(l);
f.add(p);
f.setVisible(true);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args) throws IOException {
new Client();
Socket socket = new Socket("localhost", 12000);
Scanner in = new Scanner(socket.getInputStream());
while(/* code goes here */) {
l.setText(in.nextLine());
}
}
}

private class PollingThread implements Runnable {
public void run() {
while (true) {
try {
l.setText(in.nextLine());
} catch (/* */) {
}
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
Log.d(TAG, "Thread interrupted");
}
}
}
Create a private nested class inside Client class.
Initiate the thread from Client class's main() method.
PollingThread mPollingThread = new PollingThread();
mPollingThread.start();

Need assistance java Thread slot machine

I need to make a slot machine that implements thread in java and jframe
this is what iv'e done so far kindly tell me what i need to do in order make the images change per .5 seconds when i press the the play and stop when i press stop. If all the three images are the same it'll say you won. This is what iv'e got so far how will i change this numbers or text to images in jlabel.
public class MySlotNumber extends JFrame{
private MyJLabel x;
private MyJLabel y;
private MyJLabel z;
private JButton btn;
public MySlotNumber(){
super("ABC");
setLayout(new FlowLayout());
Font font = new Font("arial",Font.ITALIC,50);
x = new MyJLabel();
x.setFont(font);
y = new MyJLabel();
y.setFont(font);
z = new MyJLabel();
z.setFont(font);
btn = new JButton("PLAY");
btn.setFont(font);
add(x);
add(y);
add(z);
add(btn);
final Thread thx = new Thread(x);
final Thread thy = new Thread(y);
final Thread thz = new Thread(z);
btn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if(e.getActionCommand().equals("PLAY")){
if(thx.isAlive()){
thx.resume();
thy.resume();
thz.resume();
} else {
thx.start();
thy.start();
thz.start();
}
btn.setText("STOP");
} else {
thx.suspend();
thy.suspend();
thz.suspend();
btn.setText("PLAY");
System.out.println(x.getText());
}
}
});
}
- - - - - - --
public class MyJLabel extends JLabel implements Runnable{
private Random r;
private int ctr;
private final int T = 500;
public MyJLabel(){
setText("0");
ctr = 0;
r= new Random();
}
#Override
public void run() {
while(true){
try {
Thread.sleep(T);
} catch (InterruptedException ex) {
Logger.getLogger(MyJLabel.class.getName()).log(Level.SEVERE, null, ex);
}
//ctr++;
ctr = r.nextInt(9)+1;
setText(String.valueOf(ctr));
}
}
}

Here is one way to put a picture on a JLabel and change it when you click a button. (I am using window builder for eclipse, so it may look a little odd.) It is not recommended you use absolute paths because when you move your project or the file, it breaks (I did this just for proof of concept).
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JLabel;
import java.awt.BorderLayout;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Test {
private JFrame frame;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Test window = new Test();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public Test() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 1379, 643);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel lblNewLabel = new JLabel("");
lblNewLabel.setIcon(new ImageIcon("C:\\Users\\Andrew\\Pictures\\Random Pictures\\Capture.JPG"));
frame.getContentPane().add(lblNewLabel, BorderLayout.CENTER);
JButton btnClickMe = new JButton("click me");
btnClickMe.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
lblNewLabel.setIcon(new ImageIcon("C:\\Users\\Andrew\\Pictures\\Random Pictures\\I'm pretty sure he did.JPG"));
}
});
frame.getContentPane().add(btnClickMe, BorderLayout.EAST);
}
}

Text not showing up in Jframes in my GUI

So I've been working on this program off and on for a few days, its a basic client server chat room. I'm trying to have it so that when you launch the client, the gui that pops up has text inside of the portnumber, servername, and textbox JTextFields. Yesterday this was the case but I've changed things and now the gui appears without text in the text fields. That code is in the displaysettings method which runs at the beginning of the try catch block. Anyone know why it isn't working?
import java.net.*;
import java.util.*;
import java.io.*;
import java.awt.event.*;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
public class clienttry2 extends JFrame implements ActionListener {
JPanel panel1 = new JPanel();
JPanel panel2 = new JPanel();
JPanel panel3 = new JPanel();
JButton send = new JButton("Send");
JButton connect = new JButton("Connect");
JLabel server = new JLabel("Server");
JLabel port = new JLabel("Port");
JButton disconnect = new JButton("Disconnect");
static JTextField servername = new JTextField(10);
static JTextField portnumber = new JTextField(10);
static JTextField textbox = new JTextField(40);
JTextArea chatbox = new JTextArea(20,45);
static Boolean isconnected = false;
static Boolean sending = false;
static Socket server1;
static ObjectInputStream in;
static ObjectOutputStream out;
public clienttry2(){
setTitle("Chat Room");
setLayout(new java.awt.FlowLayout());
setSize(600,500);
panel1.add(chatbox); //has all the chats
panel2.add(textbox); //area to type new messages into
panel2.add(send); send.addActionListener(this);//send button
panel3.add(server);
panel3.add(servername);
panel3.add(port);
panel3.add(portnumber);
panel3.add(connect); connect.addActionListener(this);
panel3.add(disconnect); disconnect.addActionListener(this); disconnect.setEnabled(false);
add(panel1);
add(panel2);
add(panel3);
}
public static void main(String[] args)throws Exception {
Client display = new Client();
display.setVisible(true);
try{
displaysettings();
connect();
setup();
String message;
message = (String) in.readObject();
System.out.println(message);
} catch (UnknownHostException e1) {
e1.printStackTrace();
} catch (IOException e1) {
e1.printStackTrace();
}
}
private static void displaysettings() {
portnumber.setText("3333");
servername.setText("localhost");
textbox.setText("This is where you type your messages to send to others on the server!");
}
private static void connect() throws UnknownHostException, IOException {
server1 = new Socket("localhost", 3333);
}
private static void setup() throws IOException {
out = new ObjectOutputStream(server1.getOutputStream());
out.flush();
in = new ObjectInputStream(server1.getInputStream());
}
public void actionPerformed(ActionEvent e){
if(e.getSource()==connect)
{
System.out.println("connected");
isconnected = true;
connect.setEnabled(false);
disconnect.setEnabled(true);
}
if(e.getSource()==send)
{
System.out.println("sending chat");
sending = true;
}
if(e.getSource()==disconnect)
{
try {
server1.close();
out.close();
isconnected = false;
connect.setEnabled(true);
disconnect.setEnabled(false);
} catch (IOException e1) {
e1.printStackTrace();
}
}
}

Swing components will not update unless told to. After you set the text, call:
textbox.repaint();
to force the GUI to update.

issue in sending the socket output to GUI

I wrote this simple multi threaded chatroom, and I am trying to send the client/server output to GUI to display it in chatroom text area but I get null pointer exception at the following line:
output.write(line + "\n");
here is the full code for GUI:
import java.awt.*;
import javax.swing.*;
import javax.swing.JTextField;
import javax.swing.JFrame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.io.IOException;
import javax.swing.JButton;
import java.io.Writer;
public class GUI {
private JFrame frame;
private JButton btnSend, btnConnect;
private JTextArea txtChat;
private JTextField fldText, fldName;
private JList clientList;
private DefaultListModel listModel;
private JScrollPane sc, scClients;
private JPanel jpS2All, jpS2Client, jpS2Text;
private String Name;
private JLabel lblErr;
private Writer output;
public GUI(String Name, Writer output) {
this.Name = Name;
this.output = output;
}
public GUI() {
}
class handler implements ActionListener, MouseListener {
handler(String Name) {
}
handler() {
}
#Override
public void actionPerformed(ActionEvent e) {
clients(); //it seems this line made the error because it creates the
listModel.addElement(Name);//gui and sends the output to textSend actionlistener
//to display it in gui
//while the output is empty, right?
//is there any way to handle this?
}
#Override
public void mouseClicked(MouseEvent e) {
fldName.setText("");
}
#Override
public void mousePressed(MouseEvent e) {
}
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
}
#Override
public void mouseExited(MouseEvent e) {
}
} //end of handler
class textSend implements ActionListener {
textSend(String Name, Writer output) {
}
#Override
public void actionPerformed(ActionEvent e) {
String line = fldText.getText();
try {
output.write(line + "\n"); // the null exception error shows the
output.flush(); // error source at this line!
} catch (IOException ioe) {
txtChat.append("Other party hung up!");
}
String contenet = Name + ":" + output;
txtChat.append(contenet);
fldText.setText("");
}
}//end of textSend
public void creatServer() {
frame = new JFrame("enter");
frame.setBounds(50, 50, 300, 200);
btnConnect = new JButton("connect");
lblErr = new JLabel();
lblErr.setText("");
frame.add(btnConnect, BorderLayout.EAST);
fldName = new JTextField();
fldName.setText("enter your name");
fldName.addMouseListener(new handler());
btnConnect.addActionListener(new handler(getName()));
frame.add(fldName, BorderLayout.CENTER);
frame.setVisible(true);
}
public void clients() { //to create the chatroom GUI
frame = new JFrame("friends");
frame.setBounds(100, 100, 400, 400);
jpS2All = new JPanel();
txtChat = new JTextArea();
txtChat.setRows(25);
txtChat.setColumns(25);
txtChat.setEditable(false);
sc = new JScrollPane(txtChat);
jpS2All.add(sc);
frame.add(jpS2All, BorderLayout.WEST);
jpS2Text = new JPanel();
////////////////////////
fldText = new JTextField();
fldText.setColumns(34);
fldText.setHorizontalAlignment(JTextField.RIGHT);
fldText.addActionListener(new textSend(getName(), output));
jpS2Text.add(fldText);
frame.add(jpS2Text, BorderLayout.SOUTH);
/////////
jpS2Client = new JPanel();
listModel = new DefaultListModel();
clientList = new JList(listModel);
clientList.setFixedCellHeight(14);
clientList.setFixedCellWidth(100);
scClients = new JScrollPane(clientList);
frame.add(jpS2Client.add(scClients), BorderLayout.EAST);
/////////
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
frame.pack();
}//end of clients
public String getName() {
Name = fldName.getText();
return Name;
}
public void appendText(final String message) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
txtChat.append(message);
}
});
}
}
server code:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;
public class server {
public void start() throws IOException {
ServerSocket serverSocket = new ServerSocket(1234);
while (true) {
Socket socket = serverSocket.accept();
ClientThread t = new ClientThread(socket);
t.start();
}
}
public static void main(String[] args) throws IOException {
server server = new server();
server.start();
}
class ClientThread extends Thread {
Socket socket;
InputStream sInput;
OutputStream sOutput;
GUI gui = new GUI();
String Name;
ClientThread(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
try {
BufferedReader sInput
= new BufferedReader(new InputStreamReader(socket.getInputStream()));
Writer sOutput = new OutputStreamWriter(socket.getOutputStream());
Name = gui.getName();
gui = new GUI(Name, sOutput);
try {
String line;
while ((line = sInput.readLine()) != null) {
gui.appendText(line);
}
} catch (IOException ex) {
Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex);
}
} catch (IOException e) {
}
}
}
}
client side:
import java.net.*;
import java.io.*;
import java.util.logging.Level;
import java.util.logging.Logger;
public class client {
private Socket s;
private String Name;
private GUI gui;
private Writer output;
private BufferedReader input;
public void start() {
try {
s = new Socket("127.0.0.1", 1234);
} catch (IOException ex) {
}
try {
input = new BufferedReader(new InputStreamReader(s.getInputStream()));
output = new OutputStreamWriter(s.getOutputStream());
} catch (IOException eIO) {
}
Name = gui.getName();
new GUI(Name, output);
new ListenFromServer().start();
}
public static void main(String[] args) {
client cl = new client();
GUI gui = new GUI();
gui.creatServer();
}
class ListenFromServer extends Thread {
public void run() {
try {
String line;
while ((line = input.readLine()) != null) {
gui.appendText(line);
}
} catch (IOException ex) {
Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
}
I know my question is a bit cumbersome but I really appreciate to help me handle this issue!

I am looking at your code and it is obvious that output is null when you attempt output.write(line + "\n"); Therefore I went and looked for the possible path of execution that could leave output un-initialized. This is where debugging comes in very handy.
Here is your execution path:
In your main method of client you create a new GUI and then call gui.creatServer();
public static void main(String[] args) {
client cl = new client();
GUI gui = new GUI();
gui.creatServer();
}
output has not been assigned and is still null
in the creatServer(); method you have this line:
fldName.addMouseListener(new handler());
which the actionPerformed method of handler calls the clients(); method which has the line:
fldText.addActionListener(new textSend(getName(), output));
note output is still null
(now your textSend class doesn't even do anything inside the constructor but that aside even if it did you are still using the output variable from the GUI class)
you have the actionPerformed method in the textSend class that has the line:
output.write(line + "\n");
Without ever initializing output it is still null, which gives you the NullPointer
Please see What is a NullPointerException, and how do I fix it? as #markspace linked in the comments. In addition you should really learn how to debug small programs.
See the following links:
http://ericlippert.com/2014/03/05/how-to-debug-small-programs/
http://blogs.msdn.com/b/smallbasic/archive/2012/10/09/how-to-debug-small-basic-programs.aspx
Again in addition, consider using Anonymous classes to ease up on those lines of code, which also makes the code easier to debug and more readable.
One last thought, remember to use standard Naming Conventions for the language you are using. your code currently has a lot of incorrect lowercase classes and some uppercase methods/properties.

the error message shows that one of the variable used in the expression was null. This may be either output or line.
As chancea already mentioned, you are calling the GUI() constructor with no arguments, so the output field is not initialized. You should remove the constructor with no arguments when you have no way to initialize the output field in it and only leave the one with arguments.

How to open a new window or switch using a button?

I'm trying to figure out this for ages, starting to wonder if it is possible!
I have a starting window for my app - I need it so that when I click on a button I have created, the window either closes and opens a new window or the window resizes and leaves just the canvas (ready to put new widgets, sprites etc... ).
I know I need a handler event for this but I just can't get the code to work.

Im not quite sure whats your question but i coded a example with a JFrame and 3 Buttons.
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
public class OpenWindowAndResizeWindow
{
private JFrame frame;
private JButton btnOpenNewWindow;
private JButton btnResizeWindow;
private JButton btnRemoveAllButtons;
/**
* Launch the application.
*/
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
try
{
OpenWindowAndResizeWindow window = new OpenWindowAndResizeWindow();
window.frame.setVisible(true);
}
catch (Exception e)
{
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public OpenWindowAndResizeWindow()
{
initialize();
}
/**
* Initialize the contents of the frame.
*/
private void initialize()
{
frame = new JFrame();
frame.setBounds(100, 100, 300, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(getBtnOpenNewWindow(), BorderLayout.NORTH);
frame.getContentPane().add(getBtnResizeWindow(), BorderLayout.SOUTH);
frame.getContentPane().add(getBtnRemoveAllButtons(), BorderLayout.CENTER);
frame.setVisible(true);
}
private void openNewWindow()
{
OpenWindowAndResizeWindow newWindow = new OpenWindowAndResizeWindow();
frame.dispose();
}
private void removeButtons()
{
getBtnOpenNewWindow().setVisible(false);
getBtnRemoveAllButtons().setVisible(false);
getBtnResizeWindow().setVisible(false);
}
private void resizeWindow()
{
Rectangle rectangle = frame.getBounds();
rectangle.width = (int)rectangle.getWidth() + 100;
rectangle.height = (int)rectangle.getHeight() + 100;
frame.setBounds(rectangle);
}
private JButton getBtnOpenNewWindow() {
if (btnOpenNewWindow == null) {
btnOpenNewWindow = new JButton("Open new Window");
btnOpenNewWindow.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
openNewWindow();
}
});
}
return btnOpenNewWindow;
}
private JButton getBtnResizeWindow() {
if (btnResizeWindow == null) {
btnResizeWindow = new JButton("Resize Window");
btnResizeWindow.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
resizeWindow();
}
});
}
return btnResizeWindow;
}
private JButton getBtnRemoveAllButtons() {
if (btnRemoveAllButtons == null) {
btnRemoveAllButtons = new JButton("Remove All Buttons");
btnRemoveAllButtons.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
removeButtons();
}
});
}
return btnRemoveAllButtons;
}
}
This code is ready to compile with javac or just paste it in your IDE.
Maybe this helps a bit. The Java SE API Documentation is useful too.