Modify Record Number in a Random Access File

Question

Hi Does anyone know if I can modify the record number in the random access file hardware.dat for each hardware record each time and update it in hardware.dat to display it? Also why does it say "Record does not exist" if I modify the record number for a hardware and try to update it but could not find that record?
Here is the code below:
// Exercise 14.11: HardwareRecord.java
package org.egan; // packaged for reuse
public class HardwareRecord
  private int recordNumber;
  private String toolName;
  private int quantity;
  private double cost;
  // no-argument constructor calls other constructor with default values
  public HardwareRecord()
    this(0,"",0,0.0); // call four-argument constructor
  } // end no-argument HardwareRecord constructor
  // initialize a record
  public HardwareRecord(int number, String tool, int amount, double price)
    setRecordNumber(number);
    setToolName(tool);
    setQuantity(amount);
    setCost(price);
  } // end four-argument HardwareRecord constructor
  // set record number
  public void setRecordNumber(int number)
    recordNumber = number;
  } // end method setRecordNumber
  // get record number
  public int getRecordNumber()
    return recordNumber;
  } // end method getRecordNumber
  // set tool name
  public void setToolName(String tool)
    toolName = tool;
  } // end method setToolName
  // get tool name
  public String getToolName()
    return toolName;
  } // end method getToolName
  // set quantity
  public void setQuantity(int amount)
    quantity = amount;
  } // end method setQuantity
  // get quantity
  public int getQuantity()
    return quantity;
  } // end method getQuantity
  // set cost
  public void setCost(double price)
    cost = price;
  } // end method setCost
  // get cost
  public double getCost()
    return cost;
  } // end method getCost
} // end class HardwareRecord-------------------------------------------------------------------------------------------------
// Exercise 14.11: RandomAccessHardwareRecord.java
// Subclass of HardwareRecord for random-access file programs.
package org.egan; // package for reuse
import java.io.RandomAccessFile;
import java.io.IOException;
public class RandomAccessHardwareRecord extends HardwareRecord
  public static final int SIZE = 46;
  // no-argument constructor calls other constructor with default values
  public RandomAccessHardwareRecord()
    this(0,"",0,0.0);
  } // end no-argument RandomAccessHardwareRecord constructor
  // initialize a RandomAccessHardwareRecord
  public RandomAccessHardwareRecord(int number, String tool, int amount, double price)
    super(number,tool,amount,price);
  } // end four-argument RandomAccessHardwareRecord constructor
  // read a record from a specified RandomAccessFile
  public void read(RandomAccessFile file) throws IOException
    setRecordNumber(file.readInt());
    setToolName(readName(file));
    setQuantity(file.readInt());
    setCost(file.readDouble());
  } // end method read
  // ensure that name is proper length
  private String readName(RandomAccessFile file) throws IOException
    char name[] = new char[15], temp;
    for(int count = 0; count < name.length; count++)
      temp = file.readChar();
      name[count] = temp;
    } // end for
    return new String(name).replace('\0',' ');
  } // end method readName
  // write a record to specified RandomAccessFile
  public void write(RandomAccessFile file) throws IOException
    file.writeInt(getRecordNumber());
    writeName(file, getToolName());
    file.writeInt(getQuantity());
    file.writeDouble(getCost());
  } // end method write
  // write a name to file; maximum of 15 characters
  private void writeName(RandomAccessFile file, String name) throws IOException
    StringBuffer buffer = null;
    if (name != null)
      buffer = new StringBuffer(name);
    else
      buffer = new StringBuffer(15);
    buffer.setLength(15);
    file.writeChars(buffer.toString());
  } // end method writeName
} // end RandomAccessHardwareRecord-------------------------------------------------------------------------------------------------
// Exercise 14.11: CreateRandomFile.java
// creates random-access file by writing 100 empty records to disk.
import java.io.IOException;
import java.io.RandomAccessFile;
import org.egan.RandomAccessHardwareRecord;
public class CreateRandomFile
  private static final int NUMBER_RECORDS = 100;
  // enable user to select file to open
  public void createFile()
    RandomAccessFile file = null;
    try  // open file for reading and writing
      file = new RandomAccessFile("hardware.dat","rw");
      RandomAccessHardwareRecord blankRecord = new RandomAccessHardwareRecord();
      // write 100 blank records
      for (int count = 0; count < NUMBER_RECORDS; count++)
        blankRecord.write(file);
      // display message that file was created
      System.out.println("Created file hardware.dat.");
      System.exit(0);  // terminate program
    } // end try
    catch (IOException ioException)
      System.err.println("Error processing file.");
      System.exit(1);
    } // end catch
    finally
      try
        if (file != null)
          file.close();  // close file
      } // end try
      catch (IOException ioException)
        System.err.println("Error closing file.");
        System.exit(1);
      } // end catch
    } // end finally
  } // end method createFile
} // end class CreateRandomFile-------------------------------------------------------------------------------------------------
// Exercise 14.11: CreateRandomFileTest.java
// Testing class CreateRandomFile
public class CreateRandomFileTest
   // main method begins program execution
   public static void main( String args[] )
     CreateRandomFile application = new CreateRandomFile();
     application.createFile();
   } // end main
} // end class CreateRandomFileTest-------------------------------------------------------------------------------------------------
// Exercise 14.11: MenuOption.java
// Defines an enum type for the hardware credit inquiry program's options.
public enum MenuOption
  // declare contents of enum type
  PRINT(1),
  UPDATE(2),
  NEW(3),
  DELETE(4),
  END(5);
  private final int value; // current menu option
  MenuOption(int valueOption)
    value = valueOption;
  } // end MenuOptions enum constructor
  public int getValue()
    return value;
  } // end method getValue
} // end enum MenuOption-------------------------------------------------------------------------------------------------
// Exercise 14.11: FileEditor.java
// This class declares methods that manipulate hardware account records
// in a random access file.
import java.io.EOFException;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Scanner;
import org.egan.RandomAccessHardwareRecord;
public class FileEditor
  RandomAccessFile file; // reference to the file
  Scanner input = new Scanner(System.in);
  // open the file
  public FileEditor(String fileName) throws IOException
    file = new RandomAccessFile(fileName, "rw");
  } // end FileEditor constructor
  // close the file
  public void closeFile() throws IOException
    if (file != null)
      file.close();
  } // end method closeFile
  // get a record from the file
  public RandomAccessHardwareRecord getRecord(int recordNumber)
     throws IllegalArgumentException, NumberFormatException, IOException
    RandomAccessHardwareRecord record = new RandomAccessHardwareRecord();
    if (recordNumber < 1 || recordNumber > 100)
      throw new IllegalArgumentException("Out of range");
    // seek appropriate record in a file
    file.seek((recordNumber - 1) * RandomAccessHardwareRecord.SIZE);
    record.read(file);
    return record;
  } // end method getRecord
  // update record tool name in file
  public void updateRecordToolName(int recordNumber, String newToolName)
     throws IllegalArgumentException, IOException
    RandomAccessHardwareRecord record = getRecord(recordNumber);
    if (record.getRecordNumber() == 0)
      throw new IllegalArgumentException("Record does not exist");
    // seek appropriate record in file
    file.seek((recordNumber - 1) * RandomAccessHardwareRecord.SIZE);
    record.setToolName(newToolName);
    record = new RandomAccessHardwareRecord(
       record.getRecordNumber(), record.getToolName(), record.getQuantity(), record.getCost());
    record.write(file); // write updated record to file
  } // end method updateRecordToolName
  // update record in file
  public void updateRecordQuantity(int recordNumber, int newQuantity)
     throws IllegalArgumentException, IOException
    RandomAccessHardwareRecord record = getRecord(recordNumber);
    if (record.getRecordNumber() == 0)
      throw new IllegalArgumentException("Record does not exist");
    // seek appropriate record in file
    file.seek((recordNumber - 1) * RandomAccessHardwareRecord.SIZE);
    record.setQuantity(newQuantity);
    record = new RandomAccessHardwareRecord(
       record.getRecordNumber(), record.getToolName(), record.getQuantity(), record.getCost());
    record.write(file); // write updated record to file
  } // end method updateRecordQuantity
  // update record in file
  public void updateRecordCost(int recordNumber, double newCost)
     throws IllegalArgumentException, IOException
    RandomAccessHardwareRecord record = getRecord(recordNumber);
    if (record.getRecordNumber() == 0)
      throw new IllegalArgumentException("Record does not exist");
    // seek appropriate record in file
    file.seek((recordNumber - 1) * RandomAccessHardwareRecord.SIZE);
    record.setCost(newCost);
    record = new RandomAccessHardwareRecord(
       record.getRecordNumber(), record.getToolName(), record.getQuantity(), record.getCost());
    record.write(file); // write updated record to file
  } // end method updateRecordCost
  // add record to file
  public void newRecord(int recordNumber, String toolName, int quantity, double cost)
     throws IllegalArgumentException, IOException
    RandomAccessHardwareRecord record = getRecord(recordNumber);
    if (record.getRecordNumber() != 0)
      throw new IllegalArgumentException("Record already exists");
    // seek appropriate record in file
    file.seek((recordNumber - 1) * RandomAccessHardwareRecord.SIZE);
    record = new RandomAccessHardwareRecord(recordNumber, toolName, quantity, cost);
    record.write(file); // write record to file
  } // end method newRecord
  // delete record from file
  public void deleteRecord(int recordNumber) throws IllegalArgumentException, IOException
    RandomAccessHardwareRecord record = getRecord(recordNumber);
    if (record.getRecordNumber() == 0)
      throw new IllegalArgumentException("Account does not exist");
    // seek appropriate record in file
    file.seek((recordNumber - 1) * RandomAccessHardwareRecord.SIZE);
    // create a blank record to write to the file
    record = new RandomAccessHardwareRecord();
    record.write(file);
  } // end method deleteRecord
  // read and display records
  public void readRecords()
    RandomAccessHardwareRecord record = new RandomAccessHardwareRecord();
    System.out.printf("%-10s%-15s%-15s%10s\n","Record","Tool Name","Quantity","Cost");
    try  // read a record and display
      file.seek(0);
      while (true)
        do
          record.read(file);
        while (record.getRecordNumber() == 0);
        // display record contents
        System.out.printf("%-10d%-15s%-15d%10.2f\n",record.getRecordNumber(),
           record.getToolName(), record.getQuantity(), record.getCost());
      } // end while
    } // end try
    catch (EOFException eofException)  // close file
      return;  // end of file was reached
    } // end catch
    catch (IOException ioException)
      System.err.println("Error reading file.");
      System.exit(1);
    } // end catch
  } // end method readRecords
} // end class FileEditor-------------------------------------------------------------------------------------------------
// Exercise 14.11: TransactionProcessor.java
// A transaction processing program using random-access files.
import java.io.IOException;
import java.util.NoSuchElementException;
import java.util.Scanner;
import org.egan.RandomAccessHardwareRecord;
public class TransactionProcessor
  private FileEditor dataFile;
  private RandomAccessHardwareRecord record;
  private MenuOption choices[] = {MenuOption.PRINT, MenuOption.UPDATE, MenuOption.NEW,
          MenuOption.DELETE, MenuOption.END};
  private Scanner input = new Scanner(System.in);
  // get the file name and open the file
  private boolean openFile()
    try // attempt to open file
      // call the helper method to open the file
      dataFile = new FileEditor("hardware.dat");
    } // end try
    catch (IOException ioException)
      System.err.println("Error opening file.");
      return false;
    } // end catch
    return true;
  } // end method openFile
  // close file and terminate application
  private void closeFile()
    try // close file
      dataFile.closeFile();
    } // end try
    catch (IOException ioException)
      System.err.println("Error closing file.");
      System.exit(1);
    } // end catch
  } // end method closeFile
  // create, update or delete the record
  private void performAction(MenuOption action)
    int recordNumber = 0;  // record number of record
    String toolName;       // tool name of the hardware instrument
    int quantity;          // total amount of items
    double cost;           // hareware tool price
    int choice;            // choose an update option   
    int newRecordNumber;   // the updated record number
    String newToolName;    // the updated tool name
    int newQuantity;       // the updated quantity
    double newCost;        // the updated cost
    try // attempt to manipulate files based on option selected
      switch(action) // switch based on option selected
        case PRINT:
          System.out.println();
          dataFile.readRecords();
          break;
        case NEW:
          System.out.printf("\n%s%s\n%s\n%s","Enter record number,",
            "tool name, quantity, and cost.","(Record number must be 1 - 100)","? ");
          recordNumber = input.nextInt();  // read record number       
          toolName = input.next();         // read tool name
          quantity = input.nextInt();      // read quantity
          cost = input.nextDouble();       // read cost
          dataFile.newRecord(recordNumber, toolName, quantity, cost); // create new record
          break;
        case UPDATE:
          System.out.print("\nEnter record number to update (1 - 100): ");
          recordNumber = input.nextInt();
          record = dataFile.getRecord(recordNumber);
          if (record.getRecordNumber() == 0)
            System.out.println("Record does not exist.");
          else
            // display record contents
            System.out.printf("%-10d%-12s%-12d%10.2f\n\n", record.getRecordNumber(),
               record.getToolName(), record.getQuantity(), record.getCost());
            System.out.printf("%s%s","\nEnter 1 to update tool name, ",
              "2 to update quantity, or 3 to update cost : ");
            choice = input.nextInt();
            if (choice == 1)
              System.out.print("Enter new record tool name : ");
              newToolName = input.next();
              dataFile.updateRecordToolName(recordNumber,newToolName); // update record
                                                                       // tool name            
              // retrieve updated record
              record = dataFile.getRecord(recordNumber);
              // display updated record
              System.out.printf("%-10d%-12s%-12d%10.2f\n", record.getRecordNumber(),
                 record.getToolName(), record.getQuantity(), record.getCost());
            else if (choice == 2)
              System.out.print("Enter new record quantity : ");
              newQuantity = input.nextInt();
              dataFile.updateRecordQuantity(recordNumber,newQuantity); // update record
                                                                       // quantity             
              // retrieve updated record
              record = dataFile.getRecord(recordNumber);
              // display updated record
              System.out.printf("%-10d%-12s%-12d%10.2f\n", record.getRecordNumber(),
                 record.getToolName(), record.getQuantity(), record.getCost());
            else if (choice == 3)
              System.out.print("Enter new record cost : ");
              newCost = input.nextDouble();
              dataFile.updateRecordCost(recordNumber,newCost); // update record cost            
              // retrieve updated record
              record = dataFile.getRecord(recordNumber);
              // display updated record
              System.out.printf("%-10d%-12s%-12d%10.2f\n", record.getRecordNumber(),
                 record.getToolName(), record.getQuantity(), record.getCost());
          } // end else     
          break;
        case DELETE:
          System.out.print("\nEnter an account to delete ( 1 - 100): ");
          recordNumber = input.nextInt();
          dataFile.deleteRecord(recordNumber);  // delete record
          break;
        default:
          System.out.println("Invalid action.");
          break;
      } // end switch
    } // end try
    catch (NumberFormatException format)
      System.err.println("Bad input.");
    } // end catch
    catch (IllegalArgumentException badRecord)
      System.err.println(badRecord.getMessage());
    } // end catch
    catch (IOException ioException)
      System.err.println("Error writing to the file.");
    } // end catch
    catch (NoSuchElementException elementException)
      System.err.println("Invalid input. Please try again.");
      input.nextLine();
    } // end catch
  } // end method performAction
  // enable user to input menu choice
  private MenuOption enterChoice()
    int menuChoice = 1;
    // display available options
    System.out.printf("\n%s\n%s\n%s\n%s\n%s\n%s","Enter your choice",
     "1 - List hardware records", "2 - Update a hardware record",
     "3 - Add a new hardware record", "4 - Delete a hardware record", "5 - End program\n?");
    try
      menuChoice = input.nextInt();
    catch (NoSuchElementException elementException)
      System.err.println("Invalid input.");
      System.exit(1);
    } // end catch
    return choices[menuChoice - 1];  // return choice from user
  } // end enterChoice
  public void processRequests()
    openFile();
    // get user's request
    MenuOption choice = enterChoice();
    while (choice != MenuOption.END)
      performAction(choice);
      choice = enterChoice();
    } // end while
    closeFile();
  } // end method processRequests
} // end class TransactionProcessor-------------------------------------------------------------------------------------------------
// Exercise 14.11: TransactionProcessorTest.java
// Testing the transaction processor.
public class TransactionProcessorTest
  public static void main(String args[])
     TransactionProcessor application = new TransactionProcessor();
     application.processRequests();
  } // end main
} // end class TransactionProcessorTest-------------------------------------------------------------------------------------------------
Below is the sample data to be entered into the random input file hardware.dat :
Record                     Tool                        Quantity                Cost
Number                   Name                
   3                      Sander                    18                         35.99
  19                      Hammer                128                      10.00
  26                      Jigsaw                   16                        14.25
  39                      Mower                    10                        79.50
  56                      Saw                        8                          89.99
  76                      Screwdriver            236                      4.99
  81                      Sledgehammer       32                        19.75
  88                      Wrench                      65                        6.48Message was edited by:
egan128
Message was edited by:
egan128
Message was edited by:
egan128

Answer 1

Hi Does anyone know if I can modify the record number
in the random access file hardware.dat for each
hardware record each time and update it in
hardware.dat to display it?If the "record number" is data that is stored in the file, then you can modify it. More precisely: it is possible to modify it.
The rest of the question had too many incompatible verbs for me to understand it.
Also why does it say
"Record does not exist" if I modify the record number
for a hardware and try to update it but could not
find that record?"Record does not exist" is a fairly reasonable error message for the situation where a program looks for a record but cannot find it. Are you asking why that particular lump of code actually does that?
(One thousand lines of code removed)