Exception in thread "main" how to solve java.lang.ArrayIndexOutOfBoundsException: 0

Question

1.i am new to java so im a noob but im trying to make this chat server and client the server so far will run but the client wont and returns the error in the title please help and try and keep it noob friendly :)

import java.net.*;
import java.io.*;
import java.awt.*;

@SuppressWarnings("serial")
class chatClient extends Frame implements Runnable
{
Socket soc;    
TextField tf;
TextArea ta;
Button btnSend,btnClose;
String sendTo;
String LoginName;
Thread t=null;
DataOutputStream dout;
DataInputStream din;
chatClient(String LoginName,String chatwith) throws Exception
{
    super(LoginName);
    this.LoginName=LoginName;
    sendTo=chatwith;
    tf=new TextField(50);
    ta=new TextArea(50,50);
    btnSend=new Button("Send");
    btnClose=new Button("Close");
    soc=new Socket("127.0.0.1",5211);

    din=new DataInputStream(soc.getInputStream()); 
    dout=new DataOutputStream(soc.getOutputStream());        
    dout.writeUTF(LoginName);

    t=new Thread(this);
    t.start();

}
@SuppressWarnings("deprecation")
void setup()
{
    setSize(600,400);
    setLayout(new GridLayout(2,1));

    add(ta);
    Panel p=new Panel();

    p.add(tf);
    p.add(btnSend);
    p.add(btnClose);
    add(p);
    show();        
}
@SuppressWarnings("deprecation")
public boolean action(Event e,Object o)
{
    if(e.arg.equals("Send"))
    {
        try
        {
            dout.writeUTF(sendTo + " "  + "DATA" + " " + tf.getText().toString());            
            ta.append("\n" + LoginName + " Says:" + tf.getText().toString());    
            tf.setText("");
        }
        catch(Exception ex)
        {
        }    
    }
    else if(e.arg.equals("Close"))
    {
        try
        {
            dout.writeUTF(LoginName + " LOGOUT");
            System.exit(1);
        }
        catch(Exception ex)
        {
        }

    }

    return super.action(e,o);
}
public static void main(String[] args) throws Exception
{
    chatClient Client=new chatClient(args[0], args[1]);
    Client.setup();                
}    
public void run()
{        
    while(true)
    {
        try
        {
            ta.append( "\n" + sendTo + " Says :" + din.readUTF());

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

http://stackoverflow.com/questions/3988788/what-is-a-stack-trace-and-how-can-i-use-it-to-debug-my-application-errors — Ming-Tang, Nov 05 '13 at 20:01

score 0 · Answer 1 · answered Nov 05 '13 at 19:59

I suspect you're starting it with:

java chatClient

You need to specify the login name and who you want to chat with, e.g.

java chatClient fred george

Otherwise args will be an empty array, so evaluating args[0] or args[1] in main will fail.

I'd also strongly advise you to fix both your indentation and your naming - follow the standard Java naming conventions.

score 0 · Answer 2 · answered Nov 05 '13 at 20:00

The only array in your program appears to be args in main. If you don't enter any command line arguments, then the array will be of length 0, and there are no elements to access.

You expect two arguments, so check the length of the array before accessing it.

if (args.length >= 2)
{
    chatClient Client=new chatClient(args[0], args[1]);
    Client.setup();   
}
else
{
    // Handle error.
}

score 0 · Answer 3 · answered Nov 05 '13 at 20:12

When instantiating the chatClient object you are specifying two elements from the args array:

chatClient Client=new chatClient(args[0], args[1]);

This array gets populated from the command line arguments. You have to specify them when invoking your program, otherwise the array will be empty:

java chatClient arg1 arg2

You can read more about specifying the command line arguments here.

As a side note, consider renaming your class so that it follows the naming conventions:

Class names should be nouns, in mixed case with the first letter of each internal word capitalized. Try to keep your class names simple and descriptive. Use whole words-avoid acronyms and abbreviations (unless the abbreviation is much more widely used than the long form, such as URL or HTML).

Exception in thread "main" how to solve java.lang.ArrayIndexOutOfBoundsException: 0

3 Answers3