bi-directional files? [resolved]

[Dillinger4]

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.

[VirtuallyVB]

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.

[Dillinger4]

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.

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);
  }
}

[VirtuallyVB]

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

  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.

[Dillinger4]

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

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.

 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);}
           }
          }

[VirtuallyVB]

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?".

[Dillinger4]

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

[Phenix]

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