a. The Rochester Bank maintains customer bank records in a random access file. W

Question

a. The Rochester Bank maintains customer bank records in a random access file. Write an application that creates 10,000 blank records and then allows the user to enter customer account information, including an account number that is 9999 or less, a last name, and a balance. Insert each new record into a data file at a location that is equal to the account number. Assume that the user will not enter invalid account numbers. Force each name to eight characters, padding it with spaces or truncating it if necessary. Also assume that the user will not enter a bank balance great than 99,000.00. Save the file as CreateBlankFile.java.

b. Create an application that uses the file created by the user in Exercise 9a and displays all existing accounts in account-number order. Save the file as ReadBankAccountsSequentially.java.

c. Create an application that uses the file created by the user in Exercise 9a and allows the user to enter an account number to view the account balance. Allow the user to view additional account balances until entering an application-terminating value. Save the file as ReadBankAccountsRandomly.java.

Explanation / Answer

CreateBankFile.java

ReadBankAccountsSequentially.java

ReadBankAccountsRandomly.java

import java.nio.file.*; import java.io.*; import java.nio.channels.FileChannel; import java.nio.ByteBuffer; import static java.nio.file.StandardOpenOption.*; import java.util.Scanner; import java.text.*; public class CreateBankFile { public static void main(String[] args) { Scanner input = new Scanner(System.in); Path filename = Paths.get("AccountRecords.txt"); Path file = filename.toAbsolutePath(); final int NUMBER_OF_RECORDS = 10000; final String ACCOUNT_NUMBER_FORMAT = "0000"; final String NAME_FORMAT = " "; final int NAME_LENGTH = NAME_FORMAT.length(); final String BALANCE_FORMAT = "00000.00"; final String delimiter = ","; String defaultRecord = ACCOUNT_NUMBER_FORMAT + delimiter + NAME_FORMAT + delimiter + BALANCE_FORMAT + System.getProperty("line.separator"); final int RECORD_SIZE = defaultRecord.length(); FileChannel fc = null; String acctString; int acct; String name; double balance; byte[] data; ByteBuffer buffer; final String QUIT = "QUIT"; createEmptyFile(file, defaultRecord, NUMBER_OF_RECORDS); try { fc = (FileChannel)Files.newByteChannel(file, CREATE, WRITE); System.out.print("Enter account number or " + QUIT + " >> "); acctString = input.nextLine(); while(!(acctString.equals(QUIT))) { acct = Integer.parseInt(acctString); System.out.print("Account holder name for account #" + acctString + " >> "); name = input.nextLine(); StringBuilder sb = new StringBuilder(name); sb.setLength(NAME_LENGTH); name = sb.toString(); System.out.print("Balance of account #" + acctString + " >> "); balance = input.nextDouble(); input.nextLine(); DecimalFormat df = new DecimalFormat(BALANCE_FORMAT); String s = acctString + delimiter + name + delimiter + df.format(balance) + System.getProperty("line.separator"); data = s.getBytes(); buffer = ByteBuffer.wrap(data); fc.position(acct * RECORD_SIZE); fc.write(buffer); System.out.print(" Enter account number or " + QUIT + " >> "); acctString = input.nextLine(); } fc.close(); } catch(Exception e) { System.out.println("Error message: " + e); } input.close(); } public static void createEmptyFile(Path file, String s, int lines) { try { OutputStream outputStr = new BufferedOutputStream(Files.newOutputStream(file, CREATE)); BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(outputStr)); for(int count = 0; count < lines; ++count) writer.write(s, 0, s.length()); writer.close(); } catch(Exception e) { System.out.println("Error message: " + e); } }

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