JScrollPane doesn't scroll when appended from outside Thread.

Question

The strangest thing I've ever seen in Java has just occured. I'm making a client program that uses an outside thread to get input from a BufferedReader that's created from a TCP/IP connection. Now, I'm using a JTextArea, that has been added into a JScrollPane. Within the main thread, if I append to my JTextArea until it reaches the end of it's view, it will scroll down to meet the newly added text. If I however instead append it remotely from a thread I've created, it will append the text, but not scroll. Does any one have any idea how I can fix this?
-Jason Thomas.

Answer 1

Your may try one of these:
1- Contruct the JScrollPane with scrollbar-policy on:
...new JScrollPane(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
2- Contruct the JTextArea with the number of rows & columns big enough to make the scrollers appear: say ...= new JTextArea(200, 200) so that you always have them
3- Call invalidate() method on the instance of the JTextArea inside the remote Thread after appending.
<main thread>
JTextArea textArea;
<remote thread>
public void run()
textArea.append(...);
textArea.invalidate();
4- If the remote Thread appends to the TextArea while the TextArea is being shown (pack), this might confuse the JScrollPane to calculate the preferredScrollableViewportSize. You may Synchronized the remote Thread. Or check this code:
<main thread>
JTextArea textArea;
<remote thread>
public void run() {
// wait until the textArea becomes visible
while ( ! textArea.isVisible() )
try {
Thread.sleep(100);
} catch (InterruptedException e) {}
// now append
textArea.append(...);