Click here to Skip to main content
Rate this: bad
good
Please Sign up or sign in to vote.
Hello there.
 
For two days i'm trying to figure out what am i doing wrong in the code bellow:
(receiving NullPointerException on actionPerformed method of sendButton, on line output.println(messageToServer);
 
public class ChatApplication implements ActionListener{
 
	//here i've declared my variables JTextAreas, clientSocket, buttons, JFrame, String userName
	
	public ChatApplication(){}
	
	public ChatApplication(String userName,String serverName) throws UnknownHostException, IOException{
		//super(userName);
//		try{
		this.userName=userName;
		clientSocket=new Socket(serverName,11111);
		input=new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
		output=new PrintWriter(new OutputStreamWriter(clientSocket.getOutputStream()),true);
		output.println(userName);
		new ServerMessageThread().start();
		
//		}catch(IOException e){
//			System.err.println(e.getMessage());
//		}
	}
	
	//creating my interface etc.
	sendButton.addActionListener(this);		
		connectButton.addActionListener(new ActionListener(){			
			public void actionPerformed(ActionEvent e){
				
				String userName=JOptionPane.showInputDialog(window,"Name: "," ",JOptionPane.PLAIN_MESSAGE);
				try{
					String serverName="localhost";
					new ChatApplication(userName, serverName);
					window.setTitle(userName);
										
				}catch(IOException ex){
					JOptionPane.showMessageDialog(window,"Clientul nu se poate conecta."+ex.getMessage().toString());
				}				
			}			
		});
		
		startServerButton.addActionListener(new ActionListener(){
			
			public void actionPerformed(ActionEvent e){
				Thread thread=new Thread(){
					public void run(){
						
						ChatServer server=new ChatServer();
						try {
							server.process();
						} catch (Exception e) {
							System.err.println(e.getMessage());
							e.printStackTrace();
						}
					}
				};
				
				thread.start();		
			}			
		});		
	}
	
	public static void main(String[] args) {
			
			ChatApplication program=new ChatApplication();
			program.createInterface();
	}
	
 
	public void actionPerformed(ActionEvent e) {
		
		if(e.getSource()==sendButton){
			sendFlag=true;
			
			try{
			String messageToServer=new String("");
			messageToServer=messageField.getText();
			//PipedOutputStream pipedOut=new PipedOutputStream();
				
			output.println(messageToServer);//<- this is where i get NullPointerException
			
			}catch(NullPointerException ex){
				System.err.println(ex.getMessage());
				ex.printStackTrace();
			}
		}
	}
	
	
	
	/*
	 * clasa se ocupa cu crearea unui thread pentru a putea citi de la server
	 */
	
	class ServerMessageThread extends Thread{
		
		
		public void run(){
			
			String serverResponse=new String();
			
				try {
					while(true){
					serverResponse=input.readLine();
					System.out.println(serverResponse);
					output.println(serverResponse); //and here sending a message to the server works
					ChatApplication.messagesTextArea.append(serverResponse+"\n");
					
					}
				} catch (IOException e) {
					ChatApplication.messagesTextArea.setForeground(Color.RED);
					ChatApplication.messagesTextArea.setText("Eroare citire de la server: "+e.getMessage());
				}
		}
	}
	
	/*
	 * clasa care se ocupa cu crearea firelor de executie a clientilor
	 */
 
}
 
When i click the sendButton i get NullPointerException. And I'm kinda stuck there. The outputStream works in the ServerMessageThread, but not when clicking my button. I know that it can be fixed, but at the moment i can't figure it out.
 
The ChatServer works, because i've tested it without using a client interface, tested it in the console. For every client i'm creating a thread.
 
I just need an idea.Thank you. Best regards.
 
P.S: i know that it isn't a good practice to put much code in the question, but i wanted to show you how i implemented the client app.
Posted 29-May-13 8:07am
Edited 29-May-13 8:48am
v4
Comments
Richard MacCutchan at 29-May-13 13:14pm
   
You need to explain which line of code this occurs on, and what are the values of the various objects and variables at the time of the error.
nameJulian at 29-May-13 13:22pm
   
The exception occurs in the actionPerformed method of sendButton, on the line: output.println(messageToServer);

1 solution

Rate this: bad
good
Please Sign up or sign in to vote.

Solution 1

public static void main(String[] args) {
			
	ChatApplication program=new ChatApplication(); //calling noarg constructor
	program.createInterface();
}
 
 
I see, You do all stream initialisation in the parameterized ctor (constructor) but you are calling the default ctor. Every thing is kept null so, NullPointerException.
 
Now here
sendButton.addActionListener(this);		
		connectButton.addActionListener(new ActionListener(){			
			public void actionPerformed(ActionEvent e){
				
				String userName=JOptionPane.showInputDialog(window,"Name: "," ",JOptionPane.PLAIN_MESSAGE);
				try{
					String serverName="localhost";
					new ChatApplication(userName, serverName); //call to appropriate constructor
					window.setTitle(userName);
										
				}catch(IOException ex){
					JOptionPane.showMessageDialog(window,"Clientul nu se poate conecta."+ex.getMessage().toString());
				}				
			}			
		});
 
 
Here you call the required ctor and start a thread, the ctor, initializes the streams and hence the calls are fine.
 
PS: Your UI is messy, do some homework.
  Permalink  
Comments
nameJulian at 30-May-13 3:28am
   
I had given up up the default constructor and called the parameterized constructor directrly intro the main method( in the constroctor calling the createInterface method), like this:
public static void main(String...args){
try{
 
String userName=JOptionPane.showInputDialog(window,"Name: "," ",JOptionPane.PLAIN_MESSAGE);
try{
String serverName="localhost";
new ChatApplication(userName, serverName); //call to appropriate constructor
window.setTitle(userName);
}catch(IOException e){
System.err.println(e.toString());
}
 
}//main
But i'm still geting the same exception.
Amitosh Swain at 30-May-13 3:40am
   
Send me your complete class (if you can), I'm really confused at your flow of code...
nameJulian at 30-May-13 6:47am
   
this is the client class:
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
 
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.border.TitledBorder;
 

public class ChatApplication implements ActionListener{
 
static JFrame window;
static Socket clientSocket;
Socket serverClientSocket;
BufferedReader input;
PrintWriter output;
static JTextArea messagesTextArea;
static JTextArea usersTextArea;
static JTextField messageField;
JButton sendButton;
JButton connectButton;
JButton startServerButton;
String userName=new String();
static boolean sendFlag=false;


public ChatApplication(){}

public ChatApplication(String userName,String serverName) throws UnknownHostException, IOException{
this.userName=userName;
clientSocket=new Socket(serverName,9999);
input=new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
output=new PrintWriter(new OutputStreamWriter(clientSocket.getOutputStream()),true);
output.println(userName);
createInterface();
new ServerMessageThread().start();
}

public void createInterface(){
window=new JFrame();
window.setSize(600,600);
window.setVisible(true);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setLayout(new BoxLayout(window.getContentPane(),BoxLayout.Y_AXIS));

sendButton=new JButton("Send");
connectButton=new JButton("Connect");
startServerButton=new JButton("Start");

messageField=new JTextField(10);
messagesTextArea=new JTextArea(40,40);
messagesTextArea.setEditable(false);
usersTextArea=new JTextArea(40,10);
usersTextArea.setEditable(false);

JScrollPane scrollPane=new JScrollPane(messagesTextArea,JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);

JPanel initialPanel=new JPanel();
initialPanel.setLayout(new BoxLayout(initialPanel,BoxLayout.X_AXIS));
initialPanel.add(connectButton);
initialPanel.add(startServerButton);

JPanel upPanel=new JPanel();
upPanel.setLayout(new BoxLayout(upPanel,BoxLayout.X_AXIS));
upPanel.setBorder(new TitledBorder(""));
upPanel.add(scrollPane);
upPanel.add(usersTextArea);

JPanel bottomPanel=new JPanel();
bottomPanel.setLayout(new BoxLayout(bottomPanel,BoxLayout.X_AXIS));
bottomPanel.setBorder(new TitledBorder(""));
bottomPanel.add(messageField);
bottomPanel.add(sendButton);

window.add(initialPanel);
window.add(upPanel);
window.add(bottomPanel);

sendButton.addActionListener(this);

// connectButton.addActionListener(new ActionListener(){
//
// public void actionPerformed(ActionEvent e){
//
// String userName=JOptionPane.showInputDialog(window,"Name: "," ",JOptionPane.PLAIN_MESSAGE);
// try{
// String serverName="localhost";
// new ChatApplication(userName, serverName);
// window.setTitle(userName);
//
// }catch(IOException ex){
// JOptionPane.showMessageDialog(window,"Clientul nu se poate conecta."+ex.getMessage().toString());
// }
//
// }
//
// });

startServerButton.addActionListener(new ActionListener(){

public void actionPerformed(ActionEvent e){
Thread thread=new Thread(){
public void run(){

ChatServer server=new ChatServer();
try {
server.process();
} catch (Exception e) {
System.err.println(e.getMessage());
e.printStackTrace();
}
}
};

thread.start();
 

}

});

}

public static void main(String[] args) {

//ChatApplication
nameJulian at 30-May-13 6:54am
   
and the continuity:
 
public static void main(String[] args) {

//ChatApplication program=new ChatApplication();
//program.createInterface();
SwingUtilities.invokeLater(new Runnable(){
public void run(){
String userName=JOptionPane.showInputDialog(window,"Name: "," ",JOptionPane.PLAIN_MESSAGE);
try{
String serverName="localhost";
new ChatApplication(userName, serverName);
window.setTitle(userName);

}catch(IOException ex){
JOptionPane.showMessageDialog(window,"Clientul nu se poate conecta."+ex.getMessage().toString());
}
}

});
}

 
public void actionPerformed(ActionEvent e) {

if(e.getSource()==sendButton){
sendFlag=true;

try{
String messageToServer=new String("");
messageToServer=messageField.getText();

output.println(messageToServer);
messageField.setText("");

}catch(NullPointerException ex){
System.err.println(ex.getMessage());
ex.printStackTrace();
}
}
}



/*
* clasa se ocupa cu crearea unui thread pentru a putea citi de la server
*/

class ServerMessageThread extends Thread{


public void run(){

String serverResponse=new String();

try {
while(true){
serverResponse=input.readLine();
messagesTextArea.append(serverResponse+"\n");
}
} catch (IOException e) {
messagesTextArea.setForeground(Color.RED);
messagesTextArea.setText("Eroare citire de la server: "+e.getMessage());
}
}
}

/*
* clasa care se ocupa cu crearea firelor de executie a clientilor
*/
 
}
Amitosh Swain at 30-May-13 7:52am
   
K thanks... I'm running it to see
Amitosh Swain at 30-May-13 7:53am
   
I'm running your code to see what's exact the problem is
Amitosh Swain at 30-May-13 8:27am
   
Sorry but I couldn't reproduce your case... I have tried connecting to the echo port (port 7) and ran the class. Got no exceptions.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

  Print Answers RSS
0 Maciej Los 310
1 OriginalGriff 285
2 Afzaal Ahmad Zeeshan 200
3 Sergey Alexandrovich Kryukov 195
4 BillWoodruff 180
0 OriginalGriff 6,499
1 Sergey Alexandrovich Kryukov 6,048
2 DamithSL 5,193
3 Manas Bhardwaj 4,657
4 Maciej Los 4,120


Advertise | Privacy | Mobile
Web03 | 2.8.1411022.1 | Last Updated 29 May 2013
Copyright © CodeProject, 1999-2014
All Rights Reserved. Terms of Service
Layout: fixed | fluid

CodeProject, 503-250 Ferrand Drive Toronto Ontario, M3C 3G8 Canada +1 416-849-8900 x 100