我可以在静态上下文中以某种方式使用非静态变量吗？

Question

I'm new in Java and I have some trouble with my code.

Is possible to use a non-static method, displayText.setText from JTextArea class in my static class Displaying ?

Thanks a lot for any kind of help!

Here's my code:

public class GUI extends javax.swing.JFrame {
    Thread send, receive, abc;
    public String x;
    private String response, nonStaticString;

    public GUI() {
        initComponents();
        abc = new Thread(new Displaying());
        abc.start();
        receive = new Thread(new Receiving(this));
        receive.start();
    }

    private static class Displaying implements Runnable {

        private final ArrayList<String> myArray = new ArrayList();
        static BlockingQueue<String> queue = new LinkedBlockingQueue();
        String s;

        @Override
        public void run() {
            while (true) {
                try {
                    s = queue.take();
                    myArray.add(s);
                    for (String myArray1 : myArray) {
                        //System.out.println(myArray1);

                        displayText.setText(myArray);

                    }

                } catch (InterruptedException ex) {
                    Logger.getLogger(GUI.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
    }

    public void setStringToShow(String stringToShow) throws InterruptedException {
        this.response = stringToShow;
        //displayText.setText(response);
        Displaying.queue.put(stringToShow);
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();
        sendButton = new javax.swing.JButton();
        getTheText = new javax.swing.JTextField();
        jLabel1 = new javax.swing.JLabel();
        jScrollPane2 = new javax.swing.JScrollPane();
        displayText = new javax.swing.JTextArea();
        jLabel2 = new javax.swing.JLabel();
        exitButtom = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        sendButton.setText("Send The Message!");
        sendButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                sendButtonActionPerformed(evt);
            }
        });

        getTheText.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                getTheTextActionPerformed(evt);
            }
        });

        jLabel1.setText("Witam w komunikatorze kliencie 2");

        displayText.setEditable(false);
        displayText.setColumns(20);
        displayText.setRows(5);
        jScrollPane2.setViewportView(displayText);
        displayText.getAccessibleContext().setAccessibleParent(this);

        jLabel2.setText("Write something to your Friend");

        exitButtom.setText("Wyjscie");
        exitButtom.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                exitButtomActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
                        .addGap(0, 182, Short.MAX_VALUE)
                        .addComponent(jLabel1)
                        .addGap(85, 85, 85)
                        .addComponent(exitButtom))
                    .addGroup(jPanel1Layout.createSequentialGroup()
                        .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(getTheText)
                            .addComponent(jScrollPane2)
                            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
                                .addGap(0, 0, Short.MAX_VALUE)
                                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                                    .addComponent(sendButton, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 215, javax.swing.GroupLayout.PREFERRED_SIZE)
                                    .addComponent(jLabel2, javax.swing.GroupLayout.Alignment.TRAILING))))
                        .addContainerGap())))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(exitButtom)
                    .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 23, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(47, 47, 47)
                .addComponent(jLabel2)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(jScrollPane2, javax.swing.GroupLayout.DEFAULT_SIZE, 176, Short.MAX_VALUE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(getTheText, javax.swing.GroupLayout.PREFERRED_SIZE, 38, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(sendButton)
                .addContainerGap())
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>                        

    private void sendButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           
        x = getTheText.getText();
        System.out.println("String: " + x);
        send = new Thread(new Sending(x));
        send.start();
        getTheText.setText("");

    }                                          

    private void getTheTextActionPerformed(java.awt.event.ActionEvent evt) {                                           
        getTheText.getText();
    }                                          

    private void exitButtomActionPerformed(java.awt.event.ActionEvent evt) {                                           
        System.exit(0);
    }                                          


    // Variables declaration - do not modify                     
    public javax.swing.JTextArea displayText;
    private javax.swing.JButton exitButtom;
    public javax.swing.JTextField getTheText;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JPanel jPanel1;
    private javax.swing.JScrollPane jScrollPane2;
    public javax.swing.JButton sendButton;
    // End of variables declaration                   

Answer 1

Make displayText a member of your GUI class and pass it to the constructor of the Displaying class.

But there's an other problem. You must not call SWING code from a non Swing thread. Have a look at SwingUtilities.invokeLater() about how to solve this problem.

Answer 2

No you can't. The code will not compile. Static methods "belong" to the class while non static variables belong to each instance of the class. When you are in the context of a class you can't know yet what the variable value will be and it might be different for several instances.

Answer 3

No, non - static variables/methods can't be used in static references. As, non-static variables depends on the state of the object while static references don't.