SWING and NETWORKING related question

[toeffy]

Hi,

I'm trying to construct a simple chat program (for learning purposes). I'm using the NetBeans IDE to construct a GUI with Swing components. I've run into a problem with printing text to a JTextPane:

Essentially, I have an actionPerformed method that contains instructions to print text to the pane, using "replaceSelection" . The program compiles and runs fine, but the text appears late. That is, other events happen first before the text appears.

Details: The problem occurs in a program for a chat Client communicating with a Chat server program. The server program is just a command line thing and works fine. The connection uses socket objects. I took all that code from somewhere else and it works fine.
My chat client has a JFrame that contains a JTextField for input, a "send" button, and a JTextPane for displaying the conversation.
When the client has entered a message, the corresponding actionPerformed method does three things:
1. It prints the message to the JTextPane
2. It transmits the message to the server program on the other machine
3. It disables the "Send" button and calls a "WaitForMessage" routine
The WaitForMessage routine contains an infinite loop ("while(true)") which terminates when a message is received from the server, prints the message to the textPane, and enables the "send" button again.

When the client types a message and clicks "send," the program appears to freeze. No text appears in the textPane until after the server has sent a message back. Once this happens, both the clients message and the server's message appear simultaneously in the textPane.

Does anyone understand why this delay occurs?

Thanks

[JosAH]

Hi,

I'm trying to construct a simple chat program (for learning purposes). I'm using the NetBeans IDE to construct a GUI with Swing components. I've run into a problem with printing text to a JTextPane:

Essentially, I have an actionPerformed method that contains instructions to print text to the pane, using "replaceSelection" . The program compiles and runs fine, but the text appears late. That is, other events happen first before the text appears.

Details: The problem occurs in a program for a chat Client communicating with a Chat server program. The server program is just a command line thing and works fine. The connection uses socket objects. I took all that code from somewhere else and it works fine.
My chat client has a JFrame that contains a JTextField for input, a "send" button, and a JTextPane for displaying the conversation.
When the client has entered a message, the corresponding actionPerformed method does three things:
1. It prints the message to the JTextPane
2. It transmits the message to the server program on the other machine
3. It disables the "Send" button and calls a "WaitForMessage" routine
The WaitForMessage routine contains an infinite loop ("while(true)") which terminates when a message is received from the server, prints the message to the textPane, and enables the "send" button again.

When the client types a message and clicks "send," the program appears to freeze. No text appears in the textPane until after the server has sent a message back. Once this happens, both the clients message and the server's message appear simultaneously in the textPane.

Does anyone understand why this delay occurs?

Thanks

You have a thread problem: Swing (and AWT) uses a single thread for all its
display tasks, event dispatching tasks and then some.

When the user presses the 'send' button your ActionListener is invoked in that
single AWT thread. Your ActionListener does quite a bit:

1) it prints that string to the JTextPane; it arrives there but your method hogs
up the AWT thread so it can't be displayed yet.

2) it transmits the string to your server so the AWT thread still can't do what
it is supposed to do, i.e. update the display of your JTextPane.

3) it disables a button (which can't be shown because the thread is still busy)
and then the poor thread has to wait for an answer from your server. When the
answer arrives you update your JTextPane again (which works) and finally
you relinguish control so everything can be visually updated.

Perform all those actions in another thread and make your ActionListener
return immediately (after it has started that other thread). That way you don't
hog the AWT thread so it can update the display when needed immediately.

kind regards,

Jos