Java Swing JTextArea和BufferedReader

Question

Can someone explain me why my app start to freeze if I try to add a text to JTextArea after reading a file by BufferedReader?

Ok. I use a GUI Designer and I have this class

public class ReaderTest {
private JPanel rootPanel;
private JTextArea textArea;
private JButton readButton;
private File file;

public static void main(String[] args) {
    SwingUtilities.invokeLater(() -> {
        JFrame frame = new JFrame("Reader");
        frame.setContentPane(new ReaderTest().rootPanel);

        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setSize(800, 600);

        frame.setVisible(true);
    });
}

private ReaderTest() {
    readButton.addActionListener(e -> {
        file = new File("/path/to/6.3MBfile");
        new Thread(new FileReader()).start();
    });
}

class FileReader implements Runnable {

    @Override
    public void run() {
        reader1();
//        reader2();
    }

    private void reader1() {
        try (InputStream inputStream = new BufferedInputStream(new FileInputStream(file))) {
            int count;

            StringBuilder str = new StringBuilder();
            while ((count = inputStream.read()) != -1) {
                str.append((char) count);
            }

            textArea.setText(str.toString());

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void reader2() {
        try (InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream(file), StandardCharsets.UTF_8);
             BufferedReader bufferedReader = new BufferedReader(inputStreamReader)) {

            String line;
            StringBuilder str = new StringBuilder();

            while ((line = bufferedReader.readLine()) != null) {
                str.append(line);
            }

            textArea.setText(str.toString());

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
}

If I read a file by BufferedInputStream (reader1), I don't have any freezes. But If I read it by BufferedReader (reader2), I get some freezes. Furthermore, my PC start to freeze after one minute and I can't simply stop my app.

Answer 1

The first thing to check is the performance for code half way between the examples - use BufferedReader.read() instead of BufferedReader.readLine() . I assume it'll have performance in the same ballpark, although there is overhead doing UTF-8 decoding.

Next up you are allocating a String each time. That's not good. Just reading a chunk with Reader.read(char[]) would be much better. Further BufferedReader.readLine() isn't very efficient, in addition to allocating the String it may also allocate a StringBuffer complete with internals every time it is call . java.nio.file.Files.readAllLines is an easy and efficient way to load a file if you want all strings, though it will be all String s.

The huge turnover of memory will be what is causing all threads to have problems.