Question

Since Java cannot unload native libraries when once used (in Matlab; see SO question), i am trying to call 2 GUI classes from within Matlab. I am working on grabbing an image from camera and then saving it on disk. I want to use one Java class for communicating with camera while another class (GUI) is still open in Matlab. Is this possible? Here’s the code:

1.

 public class GUI
    {

    public static void main(String[] args)
    {
    // Just open up the window and start things running
    MainWindow mWindow = new MainWindow();
    }

    public static void main2()
    {
        MainWindow.grabImage(0);
    }
}

2.

public class MainWindow

{

static volatile int commandVal;
        Thread updateThread;
        static CameraImage cImage;
static int fs_c =1;
    MainWindow(){

    JFrame main_f = new JFrame("M");
        main_f.getContentPane().setLayout(new BorderLayout());
        main_f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        main_f.getContentPane().add(tabPane1, "Center");

        main_f.pack();
        main_f.setVisible(true);
                kkk = 1;

        mySerial = new CameraSerial(cWindow.getPort());
}
}

3.

public static void grabImage(int commandVal){

                   while (MainWindow.kkk == 1) {
                       if (MainWindow.fs_c == 1) {
                        MainWindow.commandVal = 5;
            }
            if (MainWindow.commandVal == 5 || MainWindow.commandVal == 6){

                cImage.sendFrame(0);
                                JFileChooser save_d = new JFileChooser();
                                File saveFile = save_d.getSelectedFile();
                cImage.writeImage(saveFile + ".jpg");

                                MainWindow.fs_c = 0;
                                MainWindow.commandVal = 0;
                                mySerial.write("\r");
                                System.out.println("Camera Ready...");

break;

                        }

                else if (commandVal == -1) {
                MainWindow.commandVal = 0;
                        mySerial.write("\r");
                                status_t.setText("Camera Ready...");
            }
                       else {
                try {
                    Thread.sleep(100);

                } catch (Exception e) {
                }
            }
        }

}

From Matlab I’m calling first Gui.main([]), and then Gui.main2(). It works for the first time. But when I call Gui.main2() again, Matlab does nothing. I think it’s a bad code somewhere. Thanks for replying!

Answer 1

Just an assumption without having more information:

This check:

if (MainWindow.fs_c == 1) {
  MainWindow.commandVal = 5;
}

And later this (note that commandVal would be 5 after the check succeeded for the first time):

MainWindow.fs_c = 0;
MainWindow.commandVal = 0;

Here’s the problem:

In the first run, commandVal is set to 5, assuming MainWindow.fs_c is initially 1.
Thus MainWindow.fs_c = 0; is executed.

In the second run MainWindow.fs_c == 1 is false (MainWindow.fs_c is now 0) and MainWindow.commandVal was also set to 0. Thus the method doesn’t do anything, except sleeping for 100 milliseconds.