Understanding command line arguments

Question

Basically I am just writing a socket. For some reason I keep getting this error though

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at Main.ChatClient.main(ChatClient.java:143)

which is line " String server = args[0]; "

What does the args need to be to fix this issue?

package Main;


    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import java.awt.event.WindowAdapter;
    import java.awt.event.WindowEvent;
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.io.OutputStream;
    import java.net.Socket;
    import java.util.Observable;
    import java.util.Observer;


// Class to manage Client chat Box.
public class ChatClient {

Main a = new Main();

/** Chat client access */
static class ChatAccess extends Observable {
    private Socket socket;
    private OutputStream outputStream;

    @Override
    public void notifyObservers(Object arg) {
        super.setChanged();
        super.notifyObservers(arg);
    }

    /** Create socket, and receiving thread */
    public void InitSocket(String server, int port) throws IOException {
        socket = new Socket(server, port);
        outputStream = socket.getOutputStream();

        Thread receivingThread = new Thread() {
            @Override
            public void run() {
                try {
                    BufferedReader reader = new BufferedReader(
                            new InputStreamReader(socket.getInputStream()));
                    String line;
                    while ((line = reader.readLine()) != null)
                        notifyObservers(line);
                } catch (IOException ex) {
                    notifyObservers(ex);
                }
            }
        };
        receivingThread.start();
    }

    private static final String CRLF = "\r\n"; // newline

    /** Send a line of text */
    public void send(String text) {
        try {
            outputStream.write((text + CRLF).getBytes());
            outputStream.flush();
        } catch (IOException ex) {
            notifyObservers(ex);
        }
    }

    /** Close the socket */
    public void close() {
        try {
            socket.close();
        } catch (IOException ex) {
            notifyObservers(ex);
        }
    }
}

/** Chat client UI */
static class ChatFrame extends JFrame implements Observer {

    private JTextArea textArea;
    private JTextField inputTextField;
    private JButton sendButton;
    private ChatAccess chatAccess;

    public ChatFrame(ChatAccess chatAccess) {
        this.chatAccess = chatAccess;
        chatAccess.addObserver(this);
        buildGUI();
    }

    /** Builds the user interface */
    private void buildGUI() {
        textArea = new JTextArea(20, 50);
        textArea.setEditable(false);
        textArea.setLineWrap(true);
        add(new JScrollPane(textArea), BorderLayout.CENTER);

        Box box = Box.createHorizontalBox();
        add(box, BorderLayout.SOUTH);
        inputTextField = new JTextField();
        sendButton = new JButton("Send");
        box.add(inputTextField);
        box.add(sendButton);

        // Action for the inputTextField and the goButton
        ActionListener sendListener = new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String str = inputTextField.getText();
                if (str != null && str.trim().length() > 0)
                    chatAccess.send(str);
                inputTextField.selectAll();
                inputTextField.requestFocus();
                inputTextField.setText("");
            }
        };
        inputTextField.addActionListener(sendListener);
        sendButton.addActionListener(sendListener);

        this.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                chatAccess.close();
            }
        });
    }

    /** Updates the UI depending on the Object argument */
    public void update(Observable o, Object arg) {
        final Object finalArg = arg;
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                textArea.append(finalArg.toString());
                textArea.append("\n");
            }
        });
    }
}

public static void main(String[] args) {
    System.out.println("troll");
    String server = args[0];
    System.out.println("reached here");
    int port =2222;
    ChatAccess access = new ChatAccess();

    JFrame frame = new ChatFrame(access);
    frame.setTitle("MyChatApp - connected to " + server + ":" + port);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setResizable(false);
    frame.setVisible(true);

    try {
        access.InitSocket(server,port);
    } catch (IOException ex) {
        System.out.println("Cannot connect to " + server + ":" + port);
        ex.printStackTrace();
        System.exit(0);
    }
}
}

Brian Agnew · Accepted Answer · 2017-10-25 14:32:09Z

4

Given:

String server = args[0];

I'd suggest you provide the server name as your first argument to your program

With

public static void main(String[] args)

args is the array of command line args passed in.

answered Oct 25, 2017 at 14:32

Brian Agnew

273k38 gold badges342 silver badges443 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

k3b Over a year ago

... and ArrayIndexOutOfBoundsException: 0 indecate that there is no 0th element in the array which means the caller of your programm does not provide a commandline paramter

Collectives™ on Stack Overflow

Understanding command line arguments

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related