Edit RAF

Question

Any pointers on how to enable editing of randoms access file? Examples?
// TestRandomAccessFile.java: Store and read data, edit stored data if needed.
// using RandomAccessFile
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class TestRandomAccessFile extends JFrame {
  // Create a tabbed pane to hold two panels
  private JTabbedPane jtpStudent = new JTabbedPane();
  // Random access file for access the student.dat file
  private RandomAccessFile raf;
  /** Main method */
  public static void main(String[] args) {
    TestRandomAccessFile frame = new TestRandomAccessFile();
    frame.pack();
    frame.setTitle("Test RandomAccessFile");
    frame.setVisible(true);
  /** Default constructor */
  public TestRandomAccessFile() {
    // Open or create a random access file
    try {
      raf = new RandomAccessFile("student.dat", "rw");
    catch(IOException ex) {
      System.out.print("Error: " + ex);
      System.exit(0);
    // Place buttons in the tabbed pane
    jtpStudent.add(new RegisterStudent(raf), "Register Student");
    jtpStudent.add(new ViewStudent(raf), "View and Update Student");
    // Add the tabbed pane to the frame
    getContentPane().add(jtpStudent);
// Register student panel
class RegisterStudent extends JPanel implements ActionListener {
  // Button for registering a student
  private JButton jbtRegister;
  // Student information panel
  private StudentPanel studentPanel;
  // Random access file
  private RandomAccessFile raf;
  public RegisterStudent(RandomAccessFile raf) {
    // Pass raf to RegisterStudent Panel
    this.raf = raf;
    // Add studentPanel and jbtRegister in the panel
    setLayout(new BorderLayout());
    add(studentPanel = new StudentPanel(),
      BorderLayout.CENTER);
    add(jbtRegister = new JButton("Register"),
      BorderLayout.SOUTH);
    // Register listener
    jbtRegister.addActionListener(this);
  /** Handle button actions */
  public void actionPerformed(ActionEvent e) {
    if (e.getSource() == jbtRegister) {
      Student student = studentPanel.getStudent();
      try {
        raf.seek(raf.length());
        student.writeStudent(raf);
      catch(IOException ex) {
        System.out.print("Error: " + ex);
// View student panel
class ViewStudent extends JPanel implements ActionListener {
  // Buttons for viewing student information
  private JButton jbtFirst, jbtNext, jbtPrevious, jbtLast,jbtUpdate;
  // Random access file
  private RandomAccessFile raf = null;
  // Current student record
  private Student student = new Student();
  // Create a student panel
  private StudentPanel studentPanel = new StudentPanel();
  // File pointer in the random access file
  private long lastPos;
  private long currentPos;
  public ViewStudent(RandomAccessFile raf) {
    // Pass raf to ViewStudent
    this.raf = raf;
    // Panel p to hold four navigator buttons
    JPanel p = new JPanel();
    p.setLayout(new FlowLayout(FlowLayout.LEFT));
    p.add(jbtFirst = new JButton("First"));
    p.add(jbtNext = new JButton("Next"));
    p.add(jbtPrevious = new JButton("Previous"));
    p.add(jbtLast = new JButton("Last"));
    p.add(jbtUpdate = new JButton("Update"));
    // Add panel p and studentPanel to ViewPanel
    setLayout(new BorderLayout());
    add(studentPanel, BorderLayout.CENTER);
    add(p, BorderLayout.SOUTH);
    // Register listeners
    jbtFirst.addActionListener(this);
    jbtNext.addActionListener(this);
    jbtPrevious.addActionListener(this);
    jbtLast.addActionListener(this);
    jbtUpdate.addActionListener(this);
  /** Handle navigation button actions */
  public void actionPerformed(ActionEvent e) {
    String actionCommand = e.getActionCommand();
    if (e.getSource() instanceof JButton) {
      try {
        if ("First".equals(actionCommand)) {
          if (raf.length() > 0)
            retrieve(0);
        else if ("Next".equals(actionCommand)) {
          currentPos = raf.getFilePointer();
          if (currentPos < raf.length())
            retrieve(currentPos);
        else if ("Previous".equals(actionCommand)) {
          currentPos = raf.getFilePointer();
          if (currentPos > 0)
            retrieve(currentPos - 2*2*Student.RECORD_SIZE);
        else if ("Last".equals(actionCommand)) {
          lastPos = raf.length();
          if (lastPos > 0)
            retrieve(lastPos - 2*Student.RECORD_SIZE);
        else if ("Update".equals(actionCommand)) {
             Student student = studentPanel.getStudent();
             System.out.println("help"); //somehow make student info editable  
        ///     student.writeStudent(raf);this does nothing
      catch(IOException ex) {
        System.out.print("Error: " + ex);
  /** Retrieve a record at specified position */
  public void retrieve(long pos) {
    try {
      raf.seek(pos);
      student.readStudent(raf);
      studentPanel.setStudent(student);
    catch(IOException ex) {
      System.out.print("Error: " + ex);
// This class contains static methods for reading and writing
// fixed length records
class FixedLengthStringIO {
  // Read fixed number of characters from a DataInput stream
  public static String readFixedLengthString(int size,
    DataInput in) throws IOException {
    char c[] = new char[size];
    for (int i=0; i<size; i++)
      c[i] = in.readChar();
    return new String(c);
  // Write fixed number of characters (string s with padded spaces)
  // to a DataOutput stream
  public static void writeFixedLengthString(String s, int size,
    DataOutput out) throws IOException {
    char cBuffer[] = new char[size];
    s.getChars(0, s.length(), cBuffer, 0);
    for (int i = s.length(); i < cBuffer.length; i++)
      cBuffer[i] = ' ';
    String newS = new String(cBuffer);
    out.writeChars(newS);
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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

Answer 1

Don't think I am using seek properly I am having trouble with the update method help!
// TestRandomAccessFile.java: Store and read data
// using RandomAccessFile
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class TestRandomAccessFile extends JFrame {
  // Create a tabbed pane to hold two panels
  private JTabbedPane jtpStudent = new JTabbedPane();
  // Random access file for access the student.dat file
  private RandomAccessFile raf;
  /** Main method */
  public static void main(String[] args) {
    TestRandomAccessFile frame = new TestRandomAccessFile();
    frame.pack();
    frame.setTitle("Test RandomAccessFile");
    frame.setVisible(true);
  /** Default constructor */
  public TestRandomAccessFile() {
    // Open or create a random access file
    try {
      raf = new RandomAccessFile("student.dat", "rw");
    catch(IOException ex) {
      System.out.print("Error: " + ex);
      System.exit(0);
    // Place buttons in the tabbed pane
    jtpStudent.add(new RegisterStudent(raf), "Register Student");
    jtpStudent.add(new ViewStudent(raf), "View and Update Student");
    // Add the tabbed pane to the frame
    getContentPane().add(jtpStudent);
// Register student panel
class RegisterStudent extends JPanel implements ActionListener {
  // Button for registering a student
  private JButton jbtRegister;
  // Student information panel
  private StudentPanel studentPanel;
  // Random access file
  private RandomAccessFile raf;
  public RegisterStudent(RandomAccessFile raf) {
    // Pass raf to RegisterStudent Panel
    this.raf = raf;
    // Add studentPanel and jbtRegister in the panel
    setLayout(new BorderLayout());
    add(studentPanel = new StudentPanel(),
      BorderLayout.CENTER);
    add(jbtRegister = new JButton("Register"),
      BorderLayout.SOUTH);
    // Register listener
    jbtRegister.addActionListener(this);
  /** Handle button actions */
  public void actionPerformed(ActionEvent e) {
    if (e.getSource() == jbtRegister) {
      Student student = studentPanel.getStudent();
      try {
        raf.seek(raf.length());
        student.writeStudent(raf);
      catch(IOException ex) {
        System.out.print("Error: " + ex);
// View student panel
class ViewStudent extends JPanel implements ActionListener {
  // Buttons for viewing student information
  private JButton jbtFirst, jbtNext, jbtPrevious, jbtLast,jbtUpdate;
  // Random access file
  private RandomAccessFile raf = null;
  // Current student record
  private Student student = new Student();
  // Create a student panel
  private StudentPanel studentPanel = new StudentPanel();
  // File pointer in the random access file
  private long lastPos;
  private long currentPos;
  public ViewStudent(RandomAccessFile raf) {
    // Pass raf to ViewStudent
    this.raf = raf;
    // Panel p to hold four navigator buttons
    JPanel p = new JPanel();
    p.setLayout(new FlowLayout(FlowLayout.LEFT));
    p.add(jbtFirst = new JButton("First"));
    p.add(jbtNext = new JButton("Next"));
    p.add(jbtPrevious = new JButton("Previous"));
    p.add(jbtLast = new JButton("Last"));
    p.add(jbtUpdate = new JButton("Update"));
    // Add panel p and studentPanel to ViewPanel
    setLayout(new BorderLayout());
    add(studentPanel, BorderLayout.CENTER);
    add(p, BorderLayout.SOUTH);
    // Register listeners
    jbtFirst.addActionListener(this);
    jbtNext.addActionListener(this);
    jbtPrevious.addActionListener(this);
    jbtLast.addActionListener(this);
    jbtUpdate.addActionListener(this);
  /** Handle navigation button actions */
  public void actionPerformed(ActionEvent e) {
    String actionCommand = e.getActionCommand();
    if (e.getSource() instanceof JButton) {
      try {
        if ("First".equals(actionCommand)) {
          if (raf.length() > 0)
            retrieve(0);
        else if ("Next".equals(actionCommand)) {
          currentPos = raf.getFilePointer();
          if (currentPos < raf.length())
            retrieve(currentPos);
        else if ("Previous".equals(actionCommand)) {
          currentPos = raf.getFilePointer();
          if (currentPos > 0)
            retrieve(currentPos - 2*2*Student.RECORD_SIZE);
        else if ("Last".equals(actionCommand)) {
          lastPos = raf.length();
          if (lastPos > 0)
            retrieve(lastPos - 2*Student.RECORD_SIZE);
        else if ("Update".equals(actionCommand)) {
        currentPos = raf.getFilePointer();
          if (currentPos > 0)
            retrieve(currentPos - 1*2*Student.RECORD_SIZE);
            raf.seek(currentPos);
            Student student = studentPanel.getStudent();
                 System.out.println("edit as needed press enter"); //somehow make student info editable  
             student.writeStudent(raf);
                //private long rememberedFilePointer = -1;   not on right track?
                   //          rememberedFilePointer = raf.getFilePointer();
                // retrieve (rememberedFilePointer);//(currentPos);
      catch(IOException ex) {
        System.out.print("Error: " + ex);
  /** Retrieve a record at specified position */
  public void retrieve(long pos) {
    try {
      raf.seek(pos);
      student.readStudent(raf);
      studentPanel.setStudent(student);
    catch(IOException ex) {
      System.out.print("Error: " + ex);
// This class contains static methods for reading and writing
// fixed length records
class FixedLengthStringIO {
  // Read fixed number of characters from a DataInput stream
  public static String readFixedLengthString(int size,
    DataInput in) throws IOException {
    char c[] = new char[size];
    for (int i=0; i<size; i++)
      c[i] = in.readChar();
    return new String(c);
  // Write fixed number of characters (string s with padded spaces)
  // to a DataOutput stream
  public static void writeFixedLengthString(String s, int size,
    DataOutput out) throws IOException {
    char cBuffer[] = new char[size];
    s.getChars(0, s.length(), cBuffer, 0);
    for (int i = s.length(); i < cBuffer.length; i++)
      cBuffer[i] = ' ';
    String newS = new String(cBuffer);
    out.writeChars(newS);
// Student.java: Student class encapsulates student information
import java.io.*;
public class Student implements Serializable {
  private String name;
  private String street;
  private String city;
  private String state;
  private String zip;
  // Specify the size of five string fields in the record
  final static int NAME_SIZE = 32;
  final static int STREET_SIZE = 32;
  final static int CITY_SIZE = 20;
  final static int STATE_SIZE = 2;
  final static int ZIP_SIZE = 5;
  // the total size of the record in bytes, a Unicode
  // character is 2 bytes size
  final static int RECORD_SIZE =
    (NAME_SIZE + STREET_SIZE + CITY_SIZE + STATE_SIZE + ZIP_SIZE);
  /** Default constructor */
  public Student() {
  /** Construct a Student with specified name, street, city, state,
     and zip
  public Student(String name, String street, String city,
    String state, String zip) {
    this.name = name;
    this.street = street;
    this.city = city;
    this.state = state;
    this.zip = zip;
  /** Return name */
  public String getName() {
    return name;
  /** Return street */
  public String getStreet() {
    return street;
  /** Return city */
  public String getCity() {
    return city;
  /** Return state */
  public String getState() {
    return state;
  /** Return zip */
  public String getZip() {
    return zip;
  /** Write a student to a data output stream */
  public void writeStudent(DataOutput out) throws IOException {
    FixedLengthStringIO.writeFixedLengthString(
      name, NAME_SIZE, out);
    FixedLengthStringIO.writeFixedLengthString(
      street, STREET_SIZE, out);
    FixedLengthStringIO.writeFixedLengthString(
      city, CITY_SIZE, out);
    FixedLengthStringIO.writeFixedLengthString(
      state, STATE_SIZE, out);
    FixedLengthStringIO.writeFixedLengthString(
      zip, ZIP_SIZE, out);
  /** Read a student from data input stream */
  public void readStudent(DataInput in) throws IOException {
    name = FixedLengthStringIO.readFixedLengthString(
      NAME_SIZE, in);
    street = FixedLengthStringIO.readFixedLengthString(
      STREET_SIZE, in);
    city = FixedLengthStringIO.readFixedLengthString(
      CITY_SIZE, in);
    state = FixedLengthStringIO.readFixedLengthString(
      STATE_SIZE, in);
    zip = FixedLengthStringIO.readFixedLengthString(
      ZIP_SIZE, in);
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