bi-directional files? [resolved]

Im trying to position a file pointer from a RandomAccessFile using the public void seek(long pos ) method but an IOException stating a Negative seek offset keeps getting thrown. I should be able to go back a specific amout of bytes right? I know of other ways i could do this but i wanted to use a RandomAccessFile. :(

It looks like pos should be from 0 to length-1 in bytes. Are you trying to set a negative number for pos?

public void seek(long pos)
throws IOException
Throws:
IOException - if pos is less than 0 or if an I/O error occurs.

I created a quick app so i can track the file pointer to see where it is but for some reason the getFilePointer() method from the java.io.RandomAccess class is giving me problems. I should be getting a pointer position displayed in the second JTextField but instead nothing is displayed.

Code:

---

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

public class X {
  public static void main(String[] args){
      new Y();
  }
 }

 class Y {
    public Y(){
  JFrame jf = new JFrame("Brandon");
  JPanel jp1 = new JPanel();
  JPanel jp2 = new JPanel();
  JTextArea jta = new JTextArea(1,25);
  JTextArea jta2 = new JTextArea(1,25);
 
  Container c = jf.getContentPane(); 
  jta.addKeyListener(new Z(jta2));

  jf.addWindowListener(new WindowAdapter(){
    public void windowClosing(WindowEvent e){
      System.exit(0);
    }
  });
   
  jp1.add(jta);
  jp2.add(jta2); 
  c.add(jp1, BorderLayout.NORTH);
  c.add(jp2, BorderLayout.SOUTH);
  jf.setSize(300,300);
  jf.setVisible(true);
 }

 public static RandomAccessFile getRandom() throws IOException{
  RandomAccessFile r = new RandomAccessFile("C:\\Java\\Novice1.txt","r");
      return r;
  }
 }

class Z extends KeyAdapter {
 
  private RandomAccessFile r;
  private JTextArea jta2;
 
  public Z(JTextArea jta2){
  try{
    this.jta2 = jta2;
    r = Y.getRandom();
    }catch(IOException e){System.err.println(e);}
  }

 public void keyListener(KeyEvent ke) throws IOException{
 
    long pointer = r.getFilePointer();
    String p = String.valueOf(pointer); 
    jta2.append(p);
  }
}

---

What are you asking your new class Z (which is already a KeyAdapter) to do with the method
public void keyListener(KeyEvent ke) ?

Does a KeyAdapter have the method "keyListener"? KeyListener is an interface and keyListener is a new method you are adding (you are not overriding an existing method).

Change your Z method block
public void keyListener(KeyEvent ke) throws IOException{...

to

Code:

---

  public void keyTyped(KeyEvent ke){
  try{
    long pointer = r.getFilePointer();
    String p = String.valueOf(pointer); 
    jta2.append(p);
  }catch(IOException ioe){
    JOptionPane.showMessageDialog(null,  "Z Error:\n" + ioe, "Z.keyTyped(KeyEvent ke)", JOptionPane.ERROR_MESSAGE);
  }
  }

---

and typing into the northern textarea will cause the southern textarea to show that the filepointer is at position 0.

ok much better. I forgot that the method within the KeyAdapter class is keyTyped(). :rolleyes: Im still trying to shake the rust off. :p

I slapped this togther real quick and it works pretty good. Now at least i can see where the file pointer is and when a java.io.IOException Negative seek offset is being thrown.

Code:

---

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

public class X {
  public static void main(String[] args){
      new Y();
  }
 }

 class Y {
  public Y(){
    JFrame jf = new JFrame("Brandon");
    JPanel jp1 = new JPanel();
      JPanel jp2 = new JPanel();
      JPanel jp3 = new JPanel(); 
        JTextArea jta = new JTextArea(1,50);
        JTextArea jta2 = new JTextArea(1,50);
          JTextArea jta3 = new JTextArea(25,50);
 
  Container c = jf.getContentPane(); 
    jta.addKeyListener(new Z(jta2,jta3));
      jf.addWindowListener(new WindowAdapter(){
 
  public void windowClosing(WindowEvent e){
    System.exit(0);
  }
 });
   
  jp1.add(jta);
  jp2.add(jta2);
    jp3.add(jta3); 
    c.add(jp1, BorderLayout.NORTH);
      c.add(jp2, BorderLayout.SOUTH);
      c.add(jp3, BorderLayout.CENTER);
        jf.setSize(600,300);
        jf.setVisible(true);
  }

 public static RandomAccessFile getRandom() throws IOException{
  RandomAccessFile r = new RandomAccessFile("C:\\Java\\Novice1.txt","r");
    return r;
  }
 }

class Z extends KeyAdapter {
  private RandomAccessFile r;
    private JTextArea jta2;
    private JTextArea jta3;
      private long pointer;
 
  public Z(JTextArea jta2, JTextArea jta3){
  try{
    this.jta3 = jta3;   
    this.jta2 = jta2;
      r = Y.getRandom();
      }catch(IOException e){System.err.println(e);}
    }

 public void keyTyped(KeyEvent ke){
  try{
  char keytyped = ke.getKeyChar();
  if(keytyped == 8){
      r.seek(pointer - 1);
  }
    Character c;
    char filechar;
      pointer = r.getFilePointer();
      String p = String.valueOf(pointer); 
        jta2.append(p);
        filechar = (char) r.readByte();
          c = new Character(filechar);
          jta3.append(c.toString());
            }catch(IOException e){System.err.println(e);}
          }
          }

---

Interesting code. It reminds me of a customized "notepad.exe" that for whatever the person types, it displays something clever instead of what is being typed.

You'll get a handle on those listeners. The thing that got me in the past was, "Which listener or method should I use?".

Just wanted to say thanks. Now i can finally resolve is post. :D

I'm reborn from the ashes and getting PHP help from a young jedi. These forums sure come in handy.