LOADING TEXT FILES IN SWING
EFFICIENTLY

Suppose that you'd like to read a large text file into a Swing 
text area, using either a JTextArea or a JTextPane object. Are 
there any efficiency issues to consider in this operation?


To find out, you can set up a test program that uses
JTextComponent.read to read in a text file into a text area. Then 
experiment. Run the program specifying first a JTextArea and then
a JTextPane as the target for the text, and compare the program 
running times. Here's a program you can use to run the test:

    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
    import javax.swing.text.*;
    import java.io.*;

    public class ReadDemo {

        // read the file into the pane

        static void readin(String fn, JTextComponent pane) {
            try {
                FileReader fr = new FileReader(fn);
                pane.read(fr, null);
                fr.close();
            }
            catch (IOException e) {
                System.err.println(e);
            }
        }

        public static void main(String args[]) {
            final JFrame frame = new JFrame("Read Demo");
            frame.addWindowListener(new WindowAdapter() {
                public void windowClosing(WindowEvent e) {
                    System.exit(0);
                }
            });

            // set up the text pane, either a JTextArea or JTextPane

            final JTextComponent textpane = new JTextArea();
            file://final JTextComponent textpane = new JTextPane();

            // set up a scroll pane for the text pane

            final JScrollPane pane = new JScrollPane(textpane);
            pane.setPreferredSize(new Dimension(600, 600));

            // set up the file chooser

            String cwd = System.getProperty("user.dir");
            final JFileChooser jfc = new JFileChooser(cwd);
            final JLabel elapsed = new JLabel("Elapsed time: ");

            JButton filebutton = new JButton("Choose File");
            filebutton.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    if (jfc.showOpenDialog(frame) !=
                        JFileChooser.APPROVE_OPTION)
                            return;
                    File f = jfc.getSelectedFile();

                    // record the current time and read the file

                    final long s_time = System.currentTimeMillis();
                    frame.setCursor(Cursor.getPredefinedCursor(
                        Cursor.WAIT_CURSOR));
                    readin(f.toString(), textpane);

                    // wait for read to complete and update time

                    SwingUtilities.invokeLater(new Runnable() {
                        public void run() {
                            frame.setCursor(Cursor.
                                getPredefinedCursor(
                                Cursor.DEFAULT_CURSOR));
                            long t = System.currentTimeMillis() -
                                   s_time;
                            elapsed.setText("Elapsed time: " + t);
                        }
                    });
                }
            });

            JPanel buttonpanel = new JPanel();
            buttonpanel.add(filebutton);
            buttonpanel.add(elapsed);

            JPanel panel = new JPanel();
            panel.setLayout(new BorderLayout());
            panel.add("North", buttonpanel);
            panel.add("Center", pane);

            frame.getContentPane().add(panel);
            frame.pack();
            frame.setVisible(true);
        }
    }

The program displays a Choose File button. Click on the button, 
and a file chooser dialog appears. You can then select a text 
file to read into the text area. Depending on which of these two 
lines is uncommented:

    final JTextComponent textpane = new JTextArea();
    file://final JTextComponent textpane = new JTextPane();

the text will be read into a JTextArea or into a JTextPane. 
JTextArea supports plain text (similar to the old AWT TextArea 
class), while JTextPane handles text with attributes (such as 
underlining or italics).

The program records the time just before reading the file. 
Then it records the time after the file is read. The elapsed time
is the difference between the two times. Notice how 
SwingUtilities.invokeLater is used to display the elapsed time.
It is necessary because the read method is asynchronous, that is, 
the read operation is not complete when the method returns. Display 
updating may noticeably lag behind, because updating is done via 
events placed on the event queue, and the program calls read from 
the event dispatch thread. 

  You can demonstrate the display lag by compiling and 
  running the program after commenting out a number of
  lines:

  //    SwingUtilities.invokeLater(new Runnable() {
  //        public void run() {
              frame.setCursor(Cursor.
                  getPredefinedCursor(
                  Cursor.DEFAULT_CURSOR));
              long t = System.currentTimeMillis() -
                     s_time;
              elapsed.setText("Elapsed time: " + t);
  //         }
  //   });

  You will see that the wrong elapsed time is posted when you
  make this change. The time is calculated after read returns.
  Unfortunately, this calculation fails to account for the fact 
  that the file is still being processed for display purposes.  
  The larger the file, the more inaccurate the elapsed time 
  calculation. This problem is most pronounced when you read 
  into a JTextPane.
 
Getting back to the example program... so, there will be update 
events to process after actionPerformed returns. To deal with this 
issue, for timing purposes, SwingUtilities.invokeLater is called 
to queue a runnable task. The runnable task displays the elapsed 
time once the read/display operation is complete. The task runs 
after all the events ahead of it in the queue have been processed.

When you run the test you will see that text can be read into a
JTextArea 3-4 times faster than into a JTextPane. To make sure 
that the comparison is fair, you need to ensure that the file 
you are reading is either cached or uncached in both cases, that is, 
that both file reads are directly from disk, or else directly from 
the operating system cache.

The "bottom line" is that JTextPane does more for you than JTextArea,
but at higher cost. If you're simply interested in reading plain
text, there may be no point in paying that cost.