Java thread.sleep也使ui进入睡眠状态

Question

I im creating a simple testing app that runs a check every hour on the selected directory/s using thread.sleep() through JFileChooser. But when i select the directory and the method runs the ui panel goes grey and the swing bits disappear. The thread seems to be putting the ui to sleep as well as the method its calling.

if (option == JFileChooser.APPROVE_OPTION) {
    selectedDirectory = chooser.getSelectedFiles();
    try {
        while (true) {
            runCheck(selectedDirectory);
            Thread.sleep(1000*5);//1000 is 1 second
        }
    } catch (InterruptedException e1) {
        Thread.currentThread().interrupt();
        e1.printStackTrace();
    }               
} 

Im looking for a way around this issue so that i can print the results of the checks being run in the ui .setText(result)

Answer 1

You are correct about the code putting the UI to sleep. Since sleep is called on the Event Dispatch Thread (the thread responsible for running the gui) the UI stops processing events and 'goes to sleep'.

I think what you want is a javax.swing.Timer .

Timer t = new Timer(1000 * 5, new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        // do your reoccuring task
    }
});

This will cause your reoccurring task to be performed off of the EDT, and thus it wont leave your ui unresponsive.

Answer 2

If the code you have posted runs on the EventDispatchThread, then there is no way Swing can redraw the GUI. You're blocking (sleeping in) the thread that's supposed to handle that!

Answer 3

This is because you are running you check in the main GUI thread and are using an infinite loop. This check is a background task and should be executed in it's own thread so that the GUI can still receive and react to input by the user.

You also do not need to write your own implementation, Java has a Timer object.

Edit: There is also a Swing specific Timer object. This will have the action occur in the GUI thread, so if your task is long, it can cause the GUI to still lock up while the action is occurring (but not while it is waiting).