java - 在 "run()"方法之后我无法访问对象

Question

我正在使用 NetBeans 创建此程序。
我使用 MyMain 使用 FrameDemo 创建 JForm。 然后我将 JPanel (SensorUI SensorLL=new SensorUI) 添加到 JForm。 (请注意，我对此进行了一些简化，实际上我添加了 JPanel 的四个实例。)

面板包括一个标签“传感器”。

最终我的程序将运行一个计时器，每秒一次对传感器进行采样并在传感器标签中显示采样值。

我在传感器中有一个名为 write(value) 的方法，它将在传感器中写入(值)。

我的问题是面板的创建被 NetBeans 放置在“run()”方法中(我假设)。我可以: Sensor.write("xxx"); 如果在 run() 花句内则成功， 但如果我把 Sensor.write("xxx"); 在运行卷发之外，我得到了

cannot find symbol symbol: variable Sensor location: class MyMain

我的代码如下。我删除了很多不必要的信息，希望不要太多。 每个类都位于单独的 NetBeans 类文件中(如果有的话)。 由于某种原因，当我查看预览时，存在阴影，导致类的早期行不在阴影中。不知道最后的帖子会不会这样。如果是这样，抱歉。

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
}

<小时/>

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);

}
}

<小时/>

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">

大量 NetBeans“生成的代码”从此列表中删除 Jpanel 包含一个名为“Sensor”的 JLabel

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

Answer 1

您在错误的范围内声明了变量“SensorLL”:

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
}

您无法从运行方法外部访问它，因为在您的代码中它仅存在于运行方法内部。

编辑 我尝试更改您的 SensorUI 类以获得所需的行为。我想出了这个

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);
}
}

如果我没猜错的话，这应该完全符合你的要求。由于缺少类，我无法测试代码，因此如果发现任何错误，请说出来，我会尝试相应地更新代码。