Name: el35337 Date: 06/09/98


We had compiled the source code (see below)
for a file viewer; the frame appeared, but when
we selected a file and pressed "Open" in the
corresponding file dialog, there was a Windows
error message in java.exe, referring to a memory
location:
Memory cannot be "read"
(after having printed the address).

CODE:

/* FileViewer.java
* A program to view files in a scrollable text area.
*/
 
 
import java.io.*;
import java.awt.*;
import java.net.*;
import java.util.*;
import java.lang.*;
import java.awt.event.*;
 
/* Use the following five imports if you're using Swing as a separate API*/
 
import com.sun.java.swing.*;
import com.sun.java.swing.tree.*;
import com.sun.java.swing.border.*;
import com.sun.java.swing.event.*;
import com.sun.java.swing.text.*;
 
 
/*The class FileViewer is an extension of the Swing class JPanel. */
 
public class FileViewer extends JPanel{
 
        protected JScrollPane scrollpane;
        protected JMenuBar mainmenu;
        protected JMenu filemenu,window;
        protected JMenuItem open,exit,close,viewer;
        protected JTextArea textArea;
        protected JComboBox fileSelector;
        protected FileSelectorListener fileSelectorListener;
 
 
      private static int lastSessionViewer = 0;
 
        /*Constructor for the FileViewer class */
 
        public FileViewer() {
 
                /* Call the superclass constructor */
          super();
 
        /* Set the layout manager */
        setLayout(new BorderLayout());
                /*setLayout(new BoxLayout(this,BoxLayout.Y_AXIS));*/
 
 
 
                /*Set up the contents of the panel here */
        mainmenu = new JMenuBar();
 
                /*The File menu */
        filemenu = new JMenu("File");
 
                /*Open option in File Menu */
                open = new JMenuItem("Open");
        open.setActionCommand("open");
        open.addActionListener(new OpenActionListener());
        filemenu.add(open);
 
                /*Exit option in the File Menu */
                exit = new JMenuItem("Exit");
 
        exit.addActionListener(new ExitActionListener());
        filemenu.add(exit);
 
 
          close = new JMenuItem("Close");
 
                /*Add filemenu to the mainmenu bar*/
        mainmenu.add(filemenu);
 
        /*Window Menu*/
        window = new JMenu("Window");
 
        /*Viewer Option */
        viewer = new JMenuItem("Viewer");
        viewer.setActionCommand("viewer");
        viewer.addActionListener(new ViewerActionListener());
        window.add(viewer);
 
        /*Add window menu to mainmenu */
        mainmenu.add(window);
 
 
 
 
/* Add ScrollPanel to the window */
 
 
        textArea = new JTextArea();
 
        textArea.setFont( new Font("MonoSpaced",Font.PLAIN,12));
                //We only implement a file viewer NOT a file editor
        textArea.setEditable(false); // Rem to CHANGE TO FALSE
 
        JScrollPane scrollpane = new
JScrollPane(textArea,ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED,
                                                                ScrollPaneConsta
nts.HORIZONTAL_SCROLLBAR_AS_NEEDED);
 
 
 
 
 
 
          fileSelector = new JComboBox();
          fileSelector.setMaximumRowCount(5);
          fileSelectorListener = new FileSelectorListener();
        fileSelector.addItemListener(fileSelectorListener);
 
          this.add("North",mainmenu);
        this.add("Center",scrollpane);
          this.add("South",fileSelector);
 
    }
 
 
    /** getFrame() returns the parent frame of this file viewer panel */
    protected JFrame getFrame() {
        for (Container p = getParent(); p != null; p = p.getParent()) {
            if (p instanceof JFrame) {
                return (JFrame) p;
            }
        }
        return null;
    }
 
 
    /** Event listener class for the exit menu item */
    class ExitActionListener implements ActionListener
    {
        public void actionPerformed(ActionEvent e){
                JFrame parent = getFrame();
 
                lastSessionViewer -= 1;
                        if (lastSessionViewer == 0) {
                                        System.exit(0);
                        }
                        else {
 
 
                              parent.setVisible(false);
                        // parent.dispose();
 
                        }
 
        }
    }
 
 
    /** Event listener class for the viewer menu item */
    class ViewerActionListener implements ActionListener
    {
        public void actionPerformed(ActionEvent e){
 
                        createFileViewerFrame();
 
 
 
        }
    }
 
 
    /** Event listener class for the open menu item */
    class OpenActionListener implements ActionListener {
 
        public void actionPerformed(ActionEvent e) {
 
             JFrame frame = getFrame();
                 FileDialog fileDialog ;
 
 
                File f;
 
              fileDialog = new FileDialog(frame,"Open Dialogue",FileDialog.LOAD)
;
            fileDialog.setVisible(true);
 
 
            /* File dialog handling goes here */
                String dir = fileDialog.getDirectory();
              String file = fileDialog.getFile();
                f = new File(dir,file);
                System.out.println("Just got the file");
 
                fileDialog.dispose();
                System.out.println("File Dialog disposed");
            Thread loader = new FileLoader(f);
                System.out.println("loader initialised");
                System.out.println("Filename :" + dir+ file);
            loader.start();
 
        }
    }
 
 
    /** Event listener class for the file selector (combo box) */
    public class FileSelectorListener implements ItemListener
    {
        public void itemStateChanged(ItemEvent e)
        {
                String s = (String) fileSelector.getSelectedItem();
                File f = new File(s);
 
 
 
                Thread loader = new FileLoader(f);
                loader.start();
        }
    }
 
 
    /** FileLoader is a thread class to load in a text file, put
        its contents in a text area and update the file selector */
    class FileLoader extends Thread {
 
        File f;
 
        FileLoader(File f) {
            setPriority(4);
            this.f = f;
        }
 
        public void run() {
            if (f != null && f.isFile()) {
                int len = (int) f.length();
                if (len > 50000) {
                    System.out.println("File too large.\n");
                    return;
                }
                try {
                    Reader in = new FileReader(f);
                    char[] loadspace = new char[len];
 
                    int nch = in.read(loadspace, 0, len);
 
                    if (nch == -1) {
                        System.out.println("Could not read file.\n");
                        return;
                    }
 
                    textArea.setText(new String(loadspace, 0, nch));
 
                    int i;
                    boolean found = false;
                    String s = f.toString();
                    for (i = 0; i < fileSelector.getItemCount(); i++)
                        if (fileSelector.getItemAt(i).equals(s))
                            found = true;
System.out.println("In FileLoader");
                          System.out.println("Was file lastly opened found :" +
found);
                    fileSelector.removeItemListener(fileSelectorListener);
                    if (!found){
                         fileSelector.addItem(s);
                             System.out.println("Item Added");
                          }
 
                    fileSelector.setSelectedItem(s);
                   fileSelector.addItemListener(fileSelectorListener);
                }
                catch (Exception ex) {
                   System.out.println(ex);
                }
            }
        }
    }
 
        /*createFileViewerFrame() creates a frame, adds a new
      * file viewer panel to it, sets its size and shows it */
 
        static void createFileViewerFrame(){
 
        JFrame fr = new JFrame("Viewer");
        FileViewer f = new FileViewer();
 
                fr.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                                lastSessionViewer -=1;
                                        if (lastSessionViewer == 0) {
                                                System.exit(0);
                                        }
                        }
                }
            );
 
                fr.getContentPane().add("Center",f);
                fr.pack();
        fr.setBounds(new Rectangle(800,600));
 
        //ADD THE THING WITH RECTANGLE HERE
                fr.setVisible(true);
 
                lastSessionViewer += 1;
        }
 
    /** Main function, called on execution of the "java" command */
    public static void main(String argv[]){
 
                createFileViewerFrame();
    }
 
}
 

***************************

The application stopped working at that point.

NOTICE that the problem disappeared with JDK 1.1.5
(Review ID: 33251)
======================================================================