Question

I have some code which takes a few minutes to process, it has to connect to the web for each string in a long array, each string is a url. I want to make it so that everytime it connects, it should refresh the jtextarea so that the user is not staring into a blank page that looks frozen for 20 min. or however long it takes. here is an example of something i tried and didnt work:

try {
            ArrayList<String> myLinks = LinkParser.getmyLinksArray(jTextArea1.getText());
            for (String s : myLinks) {
                jTextArea2.append(LinkChecker.checkFileStatus(s) + "\n");
            }
        } catch (IOException ex) {
            JOptionPane.showMessageDialog(jTextArea1, "Parsing Error", "Parsing Error", JOptionPane.ERROR_MESSAGE);
            Logger.getLogger(MYView.class.getName()).log(Level.SEVERE, null, ex);
        }

Answer 1

The problem is that you need to perform the computation asynchronously. You should create a background thread that performs the computation, and then use SwingUtilities.invokeLater to update the JTextArea.

final ArrayList<String> myLinks = //...
(new Thread()
{
    public void run(){
        for (String s : myLinks) {
            try{
               final String result = LinkChecker.checkFileStatus(s) + "\n";
               SwingUtilities.invokeLater(new Runnable(){ 
                    public void run(){    
                      jtextArea2.append(result);
                    }
                });
             }catch(IOException error){
                // handle error
             }
        }
    }
}).start();

Edit
It has been pointed out that JTextArea’s append function actually is thread safe (unlike most Swing functions). Therefore, for this particular, case it is not necessary to update it via invokeLater. However, you should still do you processing in a background thread so as to allow the GUI to update, so the code is:

final ArrayList<String> myLinks = //...
(new Thread()
{
    public void run(){
        for (String s : myLinks) {
            try{
               jtextArea2.append(LinkChecker.checkFileStatus(s) + "\n");
             }catch(IOException error){
                // handle error
             }
        }
    }
}).start();

However, for pretty much any other operation that modifies a Swing object, you will need to use invokeLater (to ensure the modification occurs in the GUI thread), since almost all the Swing functions aren’t thread safe.