How to delete records from a Random-Access File?

**keith** · March 31st, 2009, 04:59 AM

I am currently studying java and i am having trouble with program to simulate a bank account. I Have most of it working but I cannot figure out how to delete records from a Random-Access File. Any help would be appreciated. I have four programs written out - Record, CreateRandomFile, WriteRandomFile and ReadRandomFile.

// Record.java
//Record class for the Random Access file program
 
import java.io.*;
 
public class Record {
    private int account;
    private String lastName;
    private String firstName;
    private double balance;
    private double overdraftlimit;
 
    //Read a record form the specified RandomAccount
public void read(RandomAccessFile file)throws IOException
{
account = file.readInt();
 
char first []=new char [15];
for (int i=0; i<first.length; i++)
first [i] = file.readChar();
 
firstName = new String (first);
 
char last [] = new char[15];
 
for (int i = 0; i<last.length; i++)
    last [i]=file.readChar();
 
lastName = new String (last);
balance = file.readDouble();
overdraftlimit = file.readDouble();
}
 
//Write a record to the specified RandomAccessFile
public void write (RandomAccessFile file) throws IOException
{
    StringBuffer buf;
 
    file.writeInt(account);
 
    if (firstName != null)
    buf = new StringBuffer (firstName);
    else
    buf = new StringBuffer(15);
 
    buf.setLength(15);
 
    file.writeChars(buf.toString());
 
    if (lastName !=null)
       buf = new StringBuffer(lastName);
       else
       buf=new StringBuffer (15);
 
       buf.setLength(15);
 
       file.writeChars(buf.toString());
       file.writeDouble(balance);
 
          file.writeDouble(overdraftlimit);
   }
 
   public void setAccount (int a){account = a;}
 
   public int getAccount() {return account;}
 
   public void setFirstName(String f) {firstName =f; }
 
   public String getFirstName () {return firstName;}
 
   public void setLastName (String l) {lastName = l;}
 
   public String getLastName () {return lastName;}
 
   public void setBalance (double b){ balance =b;}
 
   public double getBalance () {return balance;}
 
   public void setOverdraftlimit(double o) {overdraftlimit =o;}
 
   public double getOverdraftlimit () {return overdraftlimit;}
 
   //Note: This method contains a hard coded value
   //for the size of a record of information
 
   public static int size () {return 80;}
 
}

// 23.03.09
// Create Random Access file
 
import java.io.*;
 
public class CreateRandomFile {
    private Record blank;
    private RandomAccessFile file;
 
    public CreateRandomFile()
    {
        blank= new Record();
 
        try  {
            file = new RandomAccessFile ("credit.dat", "rw");
 
            for (int i=0; i<100;i++)
            blank.write(file);
        }
        catch(IOException e) {
            System.err.println("File not opened properly\n"+
                                   e.toString() );
                                   System.exit(1);
                               }
                           }
 
                           public static void main(String args[])
                           {
                               CreateRandomFile accounts = new CreateRandomFile();
                           }
                       }

import javax.swing.*;
import java.io.*;
import java.awt.*;
import java.awt.event.*;
 
public class WriteRandomFile extends Frame implements ActionListener
{
    private JTextField accountField, firstNameField,
                        lastNameField, balanceField, overdraftlimitField;
 
    private JButton enter,
                    done;
 
    private RandomAccessFile output;
    private Record data;
 
    public WriteRandomFile()
    {
        super("Write to random access file");
 
        data = new Record();
 
        try {
            output = new RandomAccessFile("credit.dat","rw");
        }
        catch ( IOException e ) {
            System.err.println(e.toString() );
            System.exit(1);
        }
 
        setSize(350,150);
        setLayout(new GridLayout(6,2));
 
        setLayout(new GridLayout(6,2));
 
        add(new JLabel("Account Number"));
        accountField = new JTextField();
        add(accountField);
 
        add(new JLabel("First Name"));
        firstNameField = new JTextField(20);
        add(firstNameField);
 
        add(new JLabel("Last Name"));
        lastNameField = new JTextField(20);
        add(lastNameField);
 
        add(new JLabel("Balance"));
        balanceField = new JTextField(20);
        add(balanceField);
 
        add(new JLabel("Overdraftlimit"));
        overdraftlimitField = new JTextField(20);
        add(overdraftlimitField);
 
 
        enter = new JButton("Enter");
        enter.addActionListener(this);
        add(enter);
 
        done = new JButton("Done");
        done.addActionListener(this);
        add(done);
 
        setVisible(true);
}
 
public void addRecord()
{
    int accountNumber = 0;
    Double d, db;
 
    if ( ! accountField.getText().equals("")) {
 
        try{
            accountNumber =
            Integer.parseInt(accountField.getText());
 
            if ( accountNumber > 0 && accountNumber <= 1000) {
                data.setAccount(accountNumber);
                data.setFirstName(firstNameField.getText());
                data.setLastName(lastNameField.getText());
                d = new Double(balanceField.getText());
                data.setBalance(d.doubleValue());
                output.seek(
                    (long) (accountNumber-1) * Record.size());
                    data.write(output);
                db = new Double(overdraftlimitField.getText());
                        data.setOverdraftlimit(db.doubleValue());
                        output.seek(
                        (long) (accountNumber-1) * Record.size());
                        data.write(output);
 
                }
 
                accountField.setText("");
                firstNameField.setText("");
                lastNameField.setText("");
                balanceField.setText("");
                overdraftlimitField.setText("");
            }
            catch (NumberFormatException nfe) {
                System.err.println(
                    "You must enter an integer account number");
                }
                catch ( IOException io){
                    System.err.println(
                        "Error during write to file\n" +
                        io.toString());
                        System.exit(1);
                    }
                }
            }
 
            public void actionPerformed( ActionEvent e)
            {
                addRecord();
 
                if (e.getSource() == done) {
                    try {
                        output.close();
                    }
                    catch ( IOException io ) {
                        System.err.println("File not closed properly\n" +
                        io.toString());
                    }
                    System.exit(0);
                }
            }
 
            public static void main(String args[])
            {
                new WriteRandomFile();
            }
        }

import javax.swing.*;
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;
 
public class ReadRandomFile extends Frame implements ActionListener
{
    private JTextField accountField, firstNameField,
                        lastNameField, balanceField, overdraftlimitField, withdrawField, lodgementField;
 
 
 
    private JButton next,
                    done,
                    withdraw,
                    lodge,
                    delete;
 
    private RandomAccessFile input;
    private Record data;
 
    private RandomAccessFile output;
 
    public ReadRandomFile()
    {
        super( "Read Client File");
 
        try {
            input = new RandomAccessFile("credit.dat","r");
        }
        catch (IOException e ) {
            System.err.println(e.toString() );
            System.exit( 1);
        }
 
        try {
                    output = new RandomAccessFile("credit.dat","rw");
                }
                catch ( IOException e ) {
                    System.err.println(e.toString() );
                    System.exit(1);
        }
 
 
 
        data = new Record();
 
        setSize(350, 150);
        setLayout(new GridLayout(10,4));
 
        add( new JLabel("Account Number") );
        accountField = new JTextField();
        accountField.setEditable(false);
        add(accountField);
 
        add(new JLabel("First Name") );
        firstNameField = new JTextField(20);
        firstNameField.setEditable(false);
        add(firstNameField);
 
        add(new JLabel("last Name") );
        lastNameField = new JTextField(20);
        lastNameField.setEditable(false);
        add(lastNameField);
 
        add(new JLabel("Balance") );
        balanceField = new JTextField(20);
        balanceField.setEditable(false);
        add(balanceField);
 
        add(new JLabel("Overdraftlimit"));
        overdraftlimitField = new JTextField(20);
        overdraftlimitField.setEditable(false);
        add(overdraftlimitField);
 
 
        next = new JButton("Next");
        next.addActionListener(this);
        add(next);
 
        done = new JButton("Done");
        done.addActionListener(this);
        add(done);
 
        add(new JLabel("Withdraw"));
        withdrawField = new JTextField(20);
        withdrawField.setEditable(true);
        add(withdrawField);
 
        add(new JLabel("Lodgement"));
        lodgementField = new JTextField(20);
        lodgementField.setEditable(true);
        add(lodgementField);
 
 
        withdraw = new JButton("Withdraw");
        withdraw.addActionListener(
                       new ActionListener() // anonymous inner class
                     {
                         // event handler called when WithdrawalJButton is pressed
                         public void actionPerformed( ActionEvent event )
                       {
                        Withdrawal( event );
                        }
 
                     } // end anonymous inner class
 
                 ); // end call to addActionListener
                 add(withdraw);
 
 
          lodge = new JButton("Lodge");
        lodge.addActionListener(
                       new ActionListener() // anonymous inner class
                     {
                     // event handler called when WithdrawalJButton is pressed
                     public void actionPerformed( ActionEvent event )
                       {
                           Lodgement( event );
                      }
 
                      } // end anonymous inner class
 
                         ); // end call to addActionListener
                 add(lodge);
 
 
        setVisible(true);
 
 
        delete = new JButton("Delete Record");
        delete.addActionListener(
            new ActionListener()
            {
                public void actionPerformed( ActionEvent event)
                {
                    DeleteRecord(event);
                }
 
            }
 
        add(delete);
 
          }
 
 
    public void actionPerformed(ActionEvent e)
    {
        int accountNumber;
 
        if (e.getSource() == next)
        readRecord();
        else
        closeFile();
}
 
 
    public void readRecord()
    {
        DecimalFormat twoDigits = new DecimalFormat("0.00");
 
        try {
            do {
                data.read(input);
            } while ( data.getAccount() == 0);
 
            accountField.setText(
                String.valueOf( data.getAccount()) );
                firstNameField.setText(data.getFirstName() );
                lastNameField.setText(data.getLastName() );
                balanceField.setText(String.valueOf(
                    twoDigits.format(data.getBalance() ) ) );
 
                    overdraftlimitField.setText(String.valueOf(
                    twoDigits.format(data.getOverdraftlimit() ) ) );
 
                }
                catch ( EOFException eof) {
                    closeFile();
                }
                catch ( IOException e ) {
                    System.err.println("error during read from file\n"+
                                    e.toString() );
                    System.exit(1);
                }
            }
 
            private void closeFile()
            {
                try {
                    input.close();
                    System.exit(0);
                }
                catch ( IOException e ) {
                    System.err.println("Error closing file\n" +
                                        e.toString() );
                    System.exit(1);
                }
            }
 
            public static void main(String args[])
            {
                new ReadRandomFile();
            }
 
                  private void Withdrawal( ActionEvent event )
                  {
                      if (Double.parseDouble(withdrawField.getText()) > Double.parseDouble(balanceField.getText() )  );
 
 
                      balanceField.setText(String.valueOf(Double.parseDouble(balanceField.getText() ) -
                                                               Double.parseDouble(withdrawField.getText() ) ) );
                            withdrawField .setText("");
 
 
 
 
                            int accountNumber = 0;
                            Double d, db;
 
 
 
                            {
 
                                try{
                                    accountNumber =
                                    Integer.parseInt(accountField.getText());
 
 
                                    {
                                        data.setAccount(accountNumber);
                                        data.setFirstName(firstNameField.getText());
                                        data.setLastName(lastNameField.getText());
                                        d = new Double(balanceField.getText());
                                        data.setBalance(d.doubleValue());
                                        output.seek(
                                            (long) (accountNumber-1) * Record.size());
                                            data.write(output);
                                        db = new Double(overdraftlimitField.getText());
                                                data.setOverdraftlimit(db.doubleValue());
                                                output.seek(
                                                (long) (accountNumber-1) * Record.size());
                                                data.write(output);
 
                                        }
 
 
                                    }
 
                                        catch ( IOException io){
 
                                                System.exit(1);
                                            }
                }
 
 
 
                   } // end method SubmitJButtonActionPerformed
 
 
                   private void Lodgement( ActionEvent event )
                   {
                       balanceField.setText(String.valueOf(Double.parseDouble(lodgementField.getText() ) +
                       Double.parseDouble(balanceField.getText() ) ) );
                           lodgementField .setText("");
 
 
                            int accountNumber = 0;
                            Double d, db;
 
 
                            {
 
                                try{
                                    accountNumber =
                                    Integer.parseInt(accountField.getText());
 
 
                                    {
                                        data.setAccount(accountNumber);
                                        data.setFirstName(firstNameField.getText());
                                        data.setLastName(lastNameField.getText());
                                        d = new Double(balanceField.getText());
                                        data.setBalance(d.doubleValue());
                                        output.seek(
                                            (long) (accountNumber-1) * Record.size());
                                            data.write(output);
                                        db = new Double(overdraftlimitField.getText());
                                                data.setOverdraftlimit(db.doubleValue());
                                                output.seek(
                                                (long) (accountNumber-1) * Record.size());
                                                data.write(output);
 
                                        }
 
 
                                    }
 
                                        catch ( IOException io){
 
                                                System.exit(1);
                                            }
                }
 
 
                    }
                    private void DeleteRecord(ActionEvent event)
                    {
 
                                }
 
}

**JavaPF** · March 31st, 2009, 09:27 AM

Hello Keith and welcome to the Java programming forums

Could you please post your 'ReadRandomFile' class again? I can't get it to compile.

Also, please always put code within the [code] [ /code] tags. (minus the space before /)

**keith** · March 31st, 2009, 09:34 AM

Sorry i going to post Read Random File again i've made couple of changes it should compile now

 
import javax.swing.*;
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;
 
public class ReadRandomFile extends Frame implements ActionListener {
    private JTextField accountField, firstNameField, lastNameField,
            balanceField, overdraftlimitField, withdrawField, lodgementField;
 
    private JButton next, done, withdraw, lodge, delete;
 
    private RandomAccessFile input;
    private Record data;
 
    private RandomAccessFile output;
 
    public ReadRandomFile() {
        super("Read Client File");
 
        try {
            input = new RandomAccessFile("credit.dat", "r");
        } catch (IOException e) {
            System.err.println(e.toString());
            System.exit(1);
        }
 
        try {
            output = new RandomAccessFile("credit.dat", "rw");
        } catch (IOException e) {
            System.err.println(e.toString());
            System.exit(1);
        }
 
        data = new Record();
 
        setSize(350, 150);
        setLayout(new GridLayout(10, 4));
 
        add(new JLabel("Account Number"));
        accountField = new JTextField();
        accountField.setEditable(false);
        add(accountField);
 
        add(new JLabel("First Name"));
        firstNameField = new JTextField(20);
        firstNameField.setEditable(false);
        add(firstNameField);
 
        add(new JLabel("last Name"));
        lastNameField = new JTextField(20);
        lastNameField.setEditable(false);
        add(lastNameField);
 
        add(new JLabel("Balance"));
        balanceField = new JTextField(20);
        balanceField.setEditable(false);
        add(balanceField);
 
        add(new JLabel("Overdraftlimit"));
        overdraftlimitField = new JTextField(20);
        overdraftlimitField.setEditable(false);
        add(overdraftlimitField);
 
        next = new JButton("Next");
        next.addActionListener(this);
        add(next);
 
        done = new JButton("Done");
        done.addActionListener(this);
        add(done);
 
        add(new JLabel("Withdraw"));
        withdrawField = new JTextField(20);
        withdrawField.setEditable(true);
        add(withdrawField);
 
        add(new JLabel("Lodgement"));
        lodgementField = new JTextField(20);
        lodgementField.setEditable(true);
        add(lodgementField);
 
        withdraw = new JButton("Withdraw");
        withdraw.addActionListener(new ActionListener() // anonymous inner class
                {
                    // event handler called when WithdrawalJButton is pressed
                    public void actionPerformed(ActionEvent event) {
                        Withdrawal(event);
                    }
 
                } // end anonymous inner class
 
                ); // end call to addActionListener
        add(withdraw);
 
        lodge = new JButton("Lodge");
        lodge.addActionListener(new ActionListener() // anonymous inner class
                {
                    // event handler called when WithdrawalJButton is pressed
                    public void actionPerformed(ActionEvent event) {
                        Lodgement(event);
                    }
 
                } // end anonymous inner class
 
                ); // end call to addActionListener
        add(lodge);
 
        setVisible(true);
 
        delete = new JButton("Delete Record");
        delete.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                DeleteRecord(event);
            }
 
        });
        add(delete);
 
    }
 
    public void actionPerformed(ActionEvent e) {
        int accountNumber;
 
        if (e.getSource() == next)
            readRecord();
        else
            closeFile();
 
    }
 
    public void readRecord() {
        DecimalFormat twoDigits = new DecimalFormat("0.00");
 
        try {
            do {
                data.read(input);
            } while (data.getAccount() == 0);
 
            accountField.setText(String.valueOf(data.getAccount()));
            firstNameField.setText(data.getFirstName());
            lastNameField.setText(data.getLastName());
            balanceField.setText(String.valueOf(twoDigits.format(data
                    .getBalance())));
 
            overdraftlimitField.setText(String.valueOf(twoDigits.format(data
                    .getOverdraftlimit())));
 
        } catch (EOFException eof) {
            closeFile();
        } catch (IOException e) {
            System.err.println("error during read from file\n" + e.toString());
            System.exit(1);
        }
    }
 
    private void closeFile() {
        try {
            input.close();
            System.exit(0);
        } catch (IOException e) {
            System.err.println("Error closing file\n" + e.toString());
            System.exit(1);
        }
    }
 
    public static void main(String args[]) {
        new ReadRandomFile();
    }
 
    private void Withdrawal(ActionEvent event) {
        double Balance = Double.parseDouble(balanceField.getText());
        double o = 0;
 
        if (Balance > o)
 
            balanceField.setText(String.valueOf(Double.parseDouble(balanceField
                    .getText())
                    - Double.parseDouble(withdrawField.getText())));
        withdrawField.setText("");
 
        if (Balance <= o) {
            JOptionPane.showMessageDialog(null,
                    "You Have Insufficant Funds to Request an Overdraft",
                    "Insufficant Funds", JOptionPane.ERROR_MESSAGE); // display
            // error
            // message
            // if
            // user
            // enters
            // invalid
            // input
            balanceField.setText("0");
        }
 
        int accountNumber = 0;
        Double d, db;
 
        {
 
            try {
                accountNumber = Integer.parseInt(accountField.getText());
 
                {
                    data.setAccount(accountNumber);
                    data.setFirstName(firstNameField.getText());
                    data.setLastName(lastNameField.getText());
                    d = new Double(balanceField.getText());
                    data.setBalance(d.doubleValue());
                    output.seek((long) (accountNumber - 1) * Record.size());
                    data.write(output);
                    db = new Double(overdraftlimitField.getText());
                    data.setOverdraftlimit(db.doubleValue());
                    output.seek((long) (accountNumber - 1) * Record.size());
                    data.write(output);
 
                }
 
            }
 
            catch (IOException io) {
 
                System.exit(1);
            }
        }
 
    } // end method SubmitJButtonActionPerformed
 
    private void Lodgement(ActionEvent event) {
        balanceField.setText(String.valueOf(Double.parseDouble(lodgementField
                .getText())
                + Double.parseDouble(balanceField.getText())));
        lodgementField.setText("");
 
        int accountNumber = 0;
        Double d, db;
 
        {
 
            try {
                accountNumber = Integer.parseInt(accountField.getText());
 
                {
                    data.setAccount(accountNumber);
                    data.setFirstName(firstNameField.getText());
                    data.setLastName(lastNameField.getText());
                    d = new Double(balanceField.getText());
                    data.setBalance(d.doubleValue());
                    output.seek((long) (accountNumber - 1) * Record.size());
                    data.write(output);
                    db = new Double(overdraftlimitField.getText());
                    data.setOverdraftlimit(db.doubleValue());
                    output.seek((long) (accountNumber - 1) * Record.size());
                    data.write(output);
 
                }
 
            }
 
            catch (IOException io) {
 
                System.exit(1);
            }
        }
 
    }
 
    private void DeleteRecord(ActionEvent event) {
 
    }
 
}

**keith** · March 31st, 2009, 09:37 AM

Sorry forgot to put [code] [ /code] tags on

**JavaPF** · March 31st, 2009, 10:01 AM

Originally Posted by keith

Sorry forgot to put [code] [ /code] tags on

No problem. I've added the code tags for you again. They keep everything tidy and makes large amounts of code easier to read.

You can easily edit your posts by clicking the EDIT button at the bottom right of your posts at any time.

**JavaPF** · March 31st, 2009, 10:09 AM

Hello Keith,

When I run 'WriteRandomFile' and create an account, nothing is stored in the credit.dat file. Did you know this?

Is this where all the account details should be stored?

**keith** · March 31st, 2009, 10:22 AM

Yeh, you need to compile the programs in this order first -
Record, CreateRandomFile, WriteRandomFile, ReadRandomFile
Than you run WriteRandomFile enter some details , click done
and run ReadRandomFile to view them

**JavaPF** · March 31st, 2009, 10:46 AM

Originally Posted by keith

Yeh, you need to compile the programs in this order first -
Record, CreateRandomFile, WriteRandomFile, ReadRandomFile
Than you run WriteRandomFile enter some details , click done
and run ReadRandomFile to view them

OK yes I see.

I inserted a record. Data is saved in credit.dat but when I view it in Notepad you can see the account details but its also full of rubbish.

**keith** · March 31st, 2009, 11:30 AM

you can see the details when you open the ReadRandomFile program, run it and click the button next to scroll thru the records you have created

**JavaPF** · March 31st, 2009, 11:35 AM

Originally Posted by keith

you can see the details when you open the ReadRandomFile program, run it and click the button next to scroll thru the records you have created

Ah OK I understand how it works now.

**Freaky Chris** · March 31st, 2009, 11:40 AM

To delete a record, you will need to read all of the data into your program, remove the record you want to delete, and then re-write it to the file. deleting file content first.

So i'd say read it all into an array list, line by line if thats how you are storing records, then you can just remove the element from the ArrayList and then write it back into the file.

Does that make sense?

EDIT: I decided I'd give you an Example

package javaapplication14;
 
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.ArrayList;
 
public class Main {
 
    public static void main(String[] args) {
        BufferedWriter bw = null;
        BufferedReader br = null;
 
        try{
            br = new BufferedReader(
                new FileReader("ex.dat")
                );
        }catch(Exception e){ System.err.println(e.getMessage()); }
 
        String temp;
        ArrayList<String> data = new ArrayList<String>();
        try{
            while((temp = br.readLine()) != null) data.add(temp);
            br.close();
        }catch(Exception e){ System.err.println(e.getMessage()); }
 
        data.remove(2);
 
        try{
            bw = new BufferedWriter(
               new FileWriter("ex.dat")
            );
 
            for(int i = 0; i < data.size(); i++){
                bw.write(data.get(i));
                bw.newLine();
            }
            bw.close();
        }catch(Exception e){ System.err.println(e.getMessage()); }
    }
}

and ex.dat could be something like this to demonstarte

Chris

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