update java swing component from different class

I am working on a crawler project using crawler4j and on top of it, I have a swing interface. I have 2 different cases, namely the controller.java (also containing the SWING components) and crawler.java. I am attempting to append output processed by the crawler.java and append it in the controller class which also holds the swing components. I tried adding an instance of the controller class into crawler class but the swing component is not showing the updates.

controller.java

//instantiate the crawler
CrawlController controller = new CrawlController(config, pageFetcher, robotstxtServer);
controller.addSeed("http://pastebin.com/");
controller.startNonBlocking(crawler.class, 1);

I also have the following method in the controller class to update the text pane:

public void setTextOP(String t){
    outputPane.setText(t);
}

In crawler.java

public class crawler extends WebCrawler {

controller c;

public crawler(controller c) {

    this.c = c;
}

@Override
public void visit(Page page) {

    int docid = page.getWebURL().getDocid();
    String url = page.getWebURL().getURL();
    String domain = page.getWebURL().getDomain();
    String subDomain = page.getWebURL().getSubDomain();
    int parentDocid = page.getWebURL().getParentDocid();

    System.out.println("Docid: " + docid);
    System.out.println("URL: " + url);
    System.out.println("Domain: '" + domain + "'");
    System.out.println("Sub-domain: '" + subDomain + "'");

    if (page.getParseData() instanceof HtmlParseData) {
        HtmlParseData htmlParseData = (HtmlParseData)page.getParseData();
        String text = htmlParseData.getText();
        String html = htmlParseData.getHtml();
        List<WebURL> links = htmlParseData.getOutgoingUrls();

        c.setTextOP(text);
      }
  }

Would really appreciate some advice on this. Thank you.

PS: the text output is printing fine in the IDE console.

It seems out that you are trying to update your UI thread from another non-GUI thread. For this cause, use the SwingUtilities.invokeLater method, which uses a Runnable to update the UI thread:

SwingUtilities.invokeLater(new Runnable() {
    public void run() {
        YourClassInstance.setTextOP("text");
      }
    }
});

I have not an exact image of your layout, but this should do the trick.

If you are making other GUI changes too - such as removing elements etc, try out revalidating and repainting your layout, in order to notify your layout manager that data are "dirty" in your swing component and its children. Check out in this question for more.