JTextArea 背景设置为透明时文本重叠

Question

I'm trying to create a transparent JTextArea but the updated text overlaps with the previous one.

I tried using scrollpane, borderlayout and setOpaque(false) method of TextArea but none of them worked.

Transparent Background - >

Here is the code

public class PanelTest {
    public static void main(String[] args) {
        PanelTest test = new PanelTest();
        test.createUI();
    }

    public void createUI() {
        JFrame frame = new JFrame("Panel Test");
        frame.setUndecorated(true);
        frame.setBackground(new Color(1.0f, 1.0f, 1.0f, 0.0f));


        JTextArea jTextArea = new JTextArea("");
        jTextArea.setEditable(false);
        jTextArea.setBackground(new Color(1.0f, 1.0f, 1.0f, 0.0f));
        jTextArea.setRows(12);
        jTextArea.setColumns(7);

        
        frame.add(jTextArea);
        frame.setResizable(true);
        frame.pack();
        frame.setVisible(true);

        Thread t = new Thread(){
            public void run(){
                while (true) {
                    
                    String s = execute("cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq");
                    System.out.println(s.length());
                    jTextArea.setText(s);
        
                    try {
                        this.sleep(2000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
        
                }
            }
        };
        t.start();
        
    }

Answer 1

Don't use a new Color(1.0f, 1.0f, 1.0f, 1.0f) in order to make the JTextArea transparent. Use setOpaque(false) instead.

Also, do not make updates to components outside of event dispatch thread. When you want to run a "heavy/long" task you should use a SwingWorker and publish updates to the UI thread (called Event dispatch thread) by using publish method. I recommend you to read Concurrency in Swing in order to understand how things should work in a Swing environment when it comes to threading.

A full example that reads terminal's output when executing java -version . Notice the process.getErrorStream . java -version command writes to error stream. You might want to change that.

public class PanelTest {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            PanelTest test = new PanelTest();
            test.createUI();
        });
    }

    public void createUI() {
        JFrame frame = new JFrame("Panel Test");
        frame.setLayout(new BorderLayout());
        frame.setUndecorated(true);
        frame.setBackground(new Color(1.0f, 1.0f, 1.0f, 0.0f));

        JTextArea jTextArea = new JTextArea("");
        jTextArea.setEditable(false);
        jTextArea.setOpaque(false);
        jTextArea.setRows(12);
        jTextArea.setColumns(7);

        frame.add(jTextArea);
        frame.setResizable(true);
        frame.pack();
        frame.setVisible(true);

        SwingWorker<Void, String> terminalReader = new SwingWorker<Void, String>() {

            @Override
            protected Void doInBackground() throws Exception {

                while (true) {
                    String s = executeTerminalCommand("java -version");
                    publish(s);
                    Thread.sleep(2000);
                }
            }

            @Override
            protected void process(List<String> chunks) {
                if (!chunks.isEmpty()) {
                    String text = chunks.get(0);
                    jTextArea.setText("");
                    jTextArea.setText(text);
                    jTextArea.repaint();
                }
            }

            @Override
            protected void done() {
                try {
                    get();
                } catch (InterruptedException | ExecutionException e) {
                    e.printStackTrace();
                }
            }
        };
        terminalReader.execute();
    }

    private static String executeTerminalCommand(String command) throws IOException {
        Process process = Runtime.getRuntime().exec(command);
        return readInputStreamAsString(process.getErrorStream());
    }

    public static String readInputStreamAsString(InputStream in) throws IOException {
        try (BufferedInputStream bis = new BufferedInputStream(in);
                ByteArrayOutputStream buf = new ByteArrayOutputStream();) {
            int result = bis.read();
            while (result != -1) {
                byte b = (byte) result;
                buf.write(b);
                result = bis.read();
            }
            return buf.toString();
        }
    }
}