java jprogressbar hangs during heavy operation

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 called, the JProgressBar is not shown until the method is over. The pro开发者_运维知识库gress bar does not interact with the method in any way (yet) and that's why I am confused. It is something like:

progressbarframe.setVisible(true); // it is a indeterminate progress bar
heavyLoadMethod();
progressbarframe.dispose();

The frame shows, but the progress bar doesn't initialize during the method. Is there any way I can solve this without using threads? What would be the simplest way?

Thank you for your time

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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.

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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.