Thread Watch

When off-loading a lengthy operation to a different thread, the preferred method of monitoring the thread's progress is to use a SwingWorker instance.

Yet another technique passes a continuation, as shown here. A similar approach is discussed in more detail by Goetz, et al. in chapter 9 of Java Concurrency in Practice. Correct synchronization in general is discussed in this video presentation Advanced Topics in Programming Languages: The Java Memory Model

With some care, the alternative approach below may be used. Having a simple MVC architecture, the Model evolves an offscreen image in a separate thread. The probability that a pixel will be modified in an iteration of the Model is given by a Random number having a Gaussian distribution. This produces the ripple effect seen below. A Swing Timer periodically notifies the View that new image data should be rendered. A Control instance allows the image to be reset and the update rate adjusted. The fill checkbox causes the Model to switch to a gray-scale palette. As the window is resized or the rate adjusted, it is easy to see the image being updated while it is also being scaled to fill the View.