What is the cause and resolution of java.lang.ExceptionInInitializerError error when trying to open a JFrame in another Thread?

Question

I\'m trying to creating a test class to open a JFrame. In order to stop the window from closing the moment the main thread finishes I added the code to open up the window in ano

Answer 1

the problem occurs when you try to set a Thread to Daemon(true). When you exit your application the thread cannot be stopped and hence throws an java.lang.IllegalStateException: Shutdown in progress

when you came over this problem you have to explicitly tell the Runtime to close the thread anyway, by adding a shotdownhook.

public void createIntegerClass() throws Exception {
    Thread t = new Thread("Test Thread") {...};

    Runtime.getRuntime().addShutdownHook(t);//explicit!
    t.start();
    t.setDaemon(true);
}