Yes - feel free to use this (it looks very useful). Note that this is not part of any default package, you need to get it... Make sure you leave the author information in the file intact (you are free to use this as long as you are not trying to pretend you wrote it!).

Remember that when processing any GUI generated event (like a button press), the GUI thread is what calls your code. This is the same thread that is responsible for updating the display, interpreting user actions, etc. If you try to do anything GUI related (like create a new window, or wait for a button press) inside the GUI thread, it won't work.

In general, if you have an event handler that does anything non-trival (like creating a window, etc), you should createa new thread to do this. This allows your event handler to return (and then the GUI thread can handle other tasks, like drawing your new window).

There are many ways to create a new thread, here is one (probably the simplest). Assume you have some code in an event handler that calls some method named createNewSongWindow(). You could start this in it's own thread like this:

Thread t = new Thread() {
  public void run() {
    createNewSongWindow();
  }
};
t.start();

Yes, just document (in your README) any code that is part of your project that you did not write, including where you got it from.