java jprogressbar hangs during heavy operation

Question

I\'m writing a java program and, before I call a method that makes heavy use of the CPU, I display a frame with a JProgressBar on it. Although I display it before the method is

Answer 1

You are blocking the EDT from repainting the GUI.

Read the section from the Swing tutorial on Concurrency in Swing for a full explanation of the problem.

Also, read the section on "How to Use Progress Bars" for a working example.

Answer 2

You should call the heavyLoadMethod in a separate thread. You can use a java.util.concurrent.Executor for it:

Executor executor = java.util.concurrent.Executors.newSingleThreadExecutor();
executor.submit(new Runnable() { public void run() { heavyLoadMethod();}});

Now the method will be called in a separate thread and the progress bar will be displayed properly.