I Can't Access Objects After “run()” Method

Question

I am using NetBeans to create this program.
I use MyMain to create a JForm using FrameDemo. Then I add a JPanel (SensorUI SensorLL=new SensorUI) to the JForm. (Note I simplified this a little, I actually add four instances of the JPanel.)

The Panel includes a Label "Sensor".

Ultimately my program will be running a timer and once a second it will sample a sensor and display the sampled value in the Sensor Label.

I have a method in Sensor called write(value) that will write (value) in Sensor.

My problem is the creation of the Panel was placed in a "run()" method by NetBeans (I assume). I can: Sensor.write("xxx"); Successfully if it is inside the run() curlys, but if I place the Sensor.write("xxx"); outside the run curlys I get

cannot find symbol symbol: variable Sensor location: class MyMain

My code is below. I removed a lot of unnecessary information, I hope not too much. Each class is in a separate NetBeans class file if that means anything. For some reason when I look at the preview there is shading that causes early lines of the classes to not be in the shading. I don't know if the final post will come out that way. If so, sorry.

public class MyMain {

public static void main(String[] args) {

    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            FrameDemo.createAndShowGUI();
            SensorUI SensorLL=new SensorUI("SensorLL");
            FrameDemo.addObject(SensorLL);
            SensorLL.writeSensor("xxx");//<<<<<This is OK
        }
    }
    );

            SensorLL.writeSensor(SensorLL, "xxx");//<<<This is not
}

---

public class FrameDemo {

  /**
 * Create the GUI and show it.  For thread safety,
 * this method should be invoked from the
 * event-dispatching thread.
 */
static        JFrame frame = new JFrame("BrewTool");  

public FrameDemo(){

}
static void createAndShowGUI() {
    //Create and set up the window.
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    frame.pack();

    frame.setVisible(true);

}
static void addObject(SensorUI Sensor){
    frame.add(Sensor);

}
}

---

public class SensorUI extends javax.swing.JPanel {

/**
 * Creates new form SensorUI
 */
public SensorUI(String title) {
    initComponents();
    Temperature.setBorder(javax.swing.BorderFactory.createTitledBorder(title));
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">

A whole lot of NetBeans "Generated Code" removed from this listing The Jpanel includes a JLabel named "Sensor"

public void writeSensor(String value){
    Sensor.setText(value);
}

Answer 1

You declared the variable 'SensorLL' in the wrong scope:

public class MyMain {

    public static void main(String[] args) {

    // Declare it in the main-method
    SensorUI SensorLL = null;

    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            FrameDemo.createAndShowGUI();

            // Here you can simply initialize it, because it's
            // already declared
            SensorLL=new SensorUI("SensorLL");
            FrameDemo.addObject(SensorLL);
            SensorLL.writeSensor("xxx");//<<<<<This is OK
        }
    }
    );

    // Works perfectly fine, because SensorLL is declared
    // outside the run-method
    SensorLL.writeSensor(SensorLL, "xxx");//<<<This is not
}

You can't access it from outside the run-method, because in your code it only exists inside the run-method.

EDIT I tried to change your SensorUI class to get the wished behaviour. I came up with this

public class SensorUI extends javax.swing.JPanel {

private Thread updateThread = null;
private boolean updateThreadIsRunning = false;

/**
 * Creates new form SensorUI
 */
public SensorUI(String title) {

    // I can't figure out what those do (mainly because of missing source code).
    initComponents();
    Temperature.setBorder(javax.swing.BorderFactory.createTitledBorder(title));

    // Create a Thread in each SensorUI which is started once the Component is
    // created and then updates the JLabel Sensor each second
    // Now each SensorUI has its own Thread which keeps updating the content of
    // the corresponding JLabel

    this.updateThread = new Thread(new Runnable() {

        @Override
        public void run() {

                updateThreadIsRunning = true;

                while(updateThreadIsRunning){
                    // The message which is shown on the Sensor JLabel
                    writeSensor("xxx");
                    try{
                        // Here you can change the update intervall in milliseconds
                        Thread.sleep(1000);
                    } catch (InterruptedException e){
                        e.printStackTrace();
                    }
                }

        }
    });

    this.updateThread.start();

}

// Here are the leftout lines

public void writeSensor(String value){
    Sensor.setText(value);
}
}

If i got you right, this should exactly do what you want. I wasn't able to test the code because of the missing classes so if find any mistakes just say something and i'll try to update the code accordingly.