Java SWT - best way to return data from components to other threads

Question

I have a Java SWT app which runs a separate thread (other than the UI) for a connection to a chat server. If I want to update components of the UI from the connection thread, I can easily do this:

        myUIclass.MyShellReference.getDisplay().asyncExec(
               new Runnable() {
                 public void run(){
                     ... update some UI component

                 }
               }
        );

My Problem is I can't find a good way to GET data from components on the UI thread. An example would be trying to create a method in my connection thread to pull a String entered into a Text box on the UI Thread...

private String getTheText(){
    final String thetext;           
    myUIclass.MyShellReference.getDisplay().asyncExec(
        new Runnable() {
              public void run(){

                    // The below wont' work because thetext is final
                        // which is required in a nested class... blah!
                        thetext = myUIclass.getTextFromSomeTextBox();
            }
         }
     );
    return thetext;
}

The problem above is that I can't actually capture what is returned from the getTextFromSomeTextBox() method, because I can only use final variables which can't be assigned. The only other solution I know is using some Atomic reference object, but there has to be a better way as I'm sure people need to do this all the time.

Any help would be greatly appreciated!!!

Answer 1

You can use some transfer object for passing variables. Very stupid example which demonstrates the idea:

private String getTheText(){
    final String[] thetext = new String[1]; //very stupid solution, but good for demonstrating the idea

    myUIclass.MyShellReference.getDisplay().syncExec( //you should use sync exec here!
        new Runnable() {
              public void run(){

                    // The below wont' work because thetext is final
                        // which is required in a nested class... blah!
                        thetext[0] = myUIclass.getTextFromSomeTextBox();
            }
         }
     );
    return thetext[0];
}

Another way is to use callbacks or Future objects.

But in reality it kind of strange approach. I would normally pass values from UI thread to the other thread, since in UI thread we know exactly what's going on, and what kind of information we are giving outside.