1. Chapter 17 – Files and Streams
Outline Introduction Data Hierarchy Files and Streams Class File Creating a Sequential-Access File Reading Data from a Sequential-Access File Updating Sequential-Access Files Random-Access Files Creating a Random-Access File Writing Data Randomly to a Random-Access File Reading Data Sequentially from a Random-Access File Case Study: A Transaction-Processing Program New I/O APIs for the Java Platform

2. 17.1 Introduction Files Long-term storage of large amounts of data
Persistent data exists after termination of program
Files stored on secondary storage devices
Magnetic disks
Optical disks
Magnetic tapes
Sequential and random access files

3. Smallest data item in a computer is a bit
17.2 Data Hierarchy
Smallest data item in a computer is a bit
Bit can be either 0 or 1
Bit short for “binary digit”
Programmers work with higher level data items
Decimal digits: (0-9)
Letters: (A-Z and a-z)
Special symbols: (e.g., %, &, *, (, ), -, +, “, :, ?, /, etc.)
Java uses Unicode characters composed of 2 bytes
A byte is 8 bits long
Fields (Java instance variables)
Composed of characters or bytes
Conveys meaning

4. File is a group of related records
17.2 Data Hierarchy
Data hierarchy
Data items in a computer form a hierarchy
Progresses from bits, to characters, to fields, etc.
Records
Composed of several fields
Implemented as a class in Java
See Fig for example
File is a group of related records
One field in each record is a record key
Record key is a unique identifier for a record
Sequential file
Records stored in order by record key

5. Fig. 17.1 Data hierarchy Randy Red 1 01001010 J u d y Judy Green Sally
Black
Tom
Blue
Iris
Orange
File
Record
Field
Byte (ASCII character J)
Bit

6. Java views a file as a stream of bytes (Fig. 17.2)
17.3 Files and Streams
Java views a file as a stream of bytes (Fig. 17.2)
File ends with end-of-file marker or a specific byte number
File as a stream of bytes associated with an object
Java also associates streams with devices
System.in, System.out, and System.err
Streams can be redirected
File processing with classes in package java.io
FileInputStream for byte-based input from a file
FileOutputStream for byte-based output to a file
FileReader for character-based input from a file
FileWriter for character-based output to a file

7. Fig. 17.2 Java’s view of a file of n bytes3
... 1 2 4 5 8 9
n-1
end-of-file marker 6 7

8. 17.3 Files and Streams Buffering Improves performance of I/O
Copies each output to a region of memory called a buffer
Entire buffer output to disk at once
One long disk access takes less time than many smaller ones
BufferedOutputStream buffers file output
BufferedInputStream buffers file input

9. Fig. 17.3 lists some useful File methods
17.4 Class File
Class File
Provides useful information about a file or directory
Does not open files or process files
Fig lists some useful File methods

10. Fig File methods

11. FileTest.java Line 5 Import java.io package
// Fig. 17.4: FileTest.java
// Demonstrating the File class.
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*; 7
public class FileTest extends JFrame
implements ActionListener { 10
private JTextField enterField;
private JTextArea outputArea; 13
// set up GUI
public FileTest() {
super( "Testing class File" ); 18
enterField = new JTextField( "Enter file or directory name here" );
enterField.addActionListener( this );
outputArea = new JTextArea(); 22
ScrollPane scrollPane = new ScrollPane();
scrollPane.add( outputArea ); 25
FileTest.java Line 5
Import java.io package

12. FileTest.java Line 38 Line 41
Container container = getContentPane();
container.add( enterField, BorderLayout.NORTH );
container.add( scrollPane, BorderLayout.CENTER ); 29
setSize( 400, 400 );
setVisible( true ); 32
} // end constructor 34
// display information about file user specifies
public void actionPerformed( ActionEvent actionEvent ) {
File name = new File( actionEvent.getActionCommand() ); 39
// if name exists, output information about it
if ( name.exists() ) {
outputArea.setText( name.getName() + " exists\n" +
( name.isFile() ? "is a file\n" : "is not a file\n" ) +
( name.isDirectory() ? "is a directory\n" :
"is not a directory\n" ) +
( name.isAbsolute() ? "is absolute path\n" :
"is not absolute path\n" ) + "Last modified: " +
name.lastModified() + "\nLength: " + name.length() +
"\nPath: " + name.getPath() + "\nAbsolute path: " +
name.getAbsolutePath() + "\nParent: " + name.getParent() ); 51
FileTest.java Line 38 Line 41
create a new File and assign it to name
Body of if outputs information about the file if it exists

13. FileTest.java Line 53 Lines 57-58 Lines 63-64
// output information if name is a file
if ( name.isFile() ) { 54
// append contents of file to outputArea
try {
BufferedReader input = new BufferedReader(
new FileReader( name ) );
StringBuffer buffer = new StringBuffer();
String text;
outputArea.append( "\n\n" ); 62
while ( ( text = input.readLine() ) != null )
buffer.append( text + "\n" ); 65
outputArea.append( buffer.toString() ); } 68
// process file processing problems
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "FILE ERROR",
"FILE ERROR", JOptionPane.ERROR_MESSAGE ); } 74
} // end if 76
Test if our object is a file
FileTest.java Line 53 Lines Lines 63-64
Create reader to gather data from the file
Read text until there is no more in the file

14. FileTest.java Line 79 Lines 91-93
// output directory listing
else if ( name.isDirectory() ) {
String directory[] = name.list(); 80
outputArea.append( "\n\nDirectory contents:\n"); 82
for ( int i = 0; i < directory.length; i++ )
outputArea.append( directory[ i ] + "\n" ); } 86
} // end outer if 88
// not file or directory, output error message
else {
JOptionPane.showMessageDialog( this,
actionEvent.getActionCommand() + " Does Not Exist",
"ERROR", JOptionPane.ERROR_MESSAGE ); } 95
} // end method actionPerformed 97
public static void main( String args[] ) {
FileTest application = new FileTest();
application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); }
103
104 } // end class FileTest
Get a list of the files in the directory
FileTest.java Line 79 Lines 91-93
If file does not exist, display error

15. FileTest.java

16. 17.5 Creating a Sequential-Access File
Java Files
Java imposes no structure on a file
Programmer structures file according to application
Following program uses simple record structure

17. BankUI.java Line 3 Line 8 Line 17
// Fig. 17.5: BankUI.java
// A reusable GUI for the examples in this chapter.
package com.deitel.jhtp5.ch17; 4
import java.awt.*;
import javax.swing.*; 7
public class BankUI extends JPanel { 9
// label text for GUI
protected final static String names[] = { "Account number",
"First name", "Last name", "Balance", "Transaction Amount" }; 13
// GUI components; protected for future subclass access
protected JLabel labels[];
protected JTextField fields[];
protected JButton doTask1, doTask2;
protected JPanel innerPanelCenter, innerPanelSouth; 19
protected int size; // number of text fields in GUI 21
// constants representing text fields in GUI
public static final int ACCOUNT = 0, FIRSTNAME = 1, LASTNAME = 2,
BALANCE = 3, TRANSACTION = 4; 25
Compile this class in a package for reuse
BankUI.java Line 3 Line 8 Line 17
Bank GUI for all examples in this chapter
These buttons will perform actions in later examples

18. 26 // Set up GUI. Constructor argument size determines the number of
// rows of GUI components.
public BankUI( int mySize ) {
size = mySize;
labels = new JLabel[ size ];
fields = new JTextField[ size ]; 33
// create labels
for ( int count = 0; count < labels.length; count++ )
labels[ count ] = new JLabel( names[ count ] ); 37
// create text fields
for ( int count = 0; count < fields.length; count++ )
fields[ count ] = new JTextField(); 41
// create panel to lay out labels and fields
innerPanelCenter = new JPanel();
innerPanelCenter.setLayout( new GridLayout( size, 2 ) ); 45
// attach labels and fields to innerPanelCenter
for ( int count = 0; count < size; count++ ) {
innerPanelCenter.add( labels[ count ] );
innerPanelCenter.add( fields[ count ] ); } 51
BankUI.java

19. Return the task buttons
// create generic buttons; no labels or event handlers
doTask1 = new JButton();
doTask2 = new JButton(); 55
// create panel to lay out buttons and attach buttons
innerPanelSouth = new JPanel();
innerPanelSouth.add( doTask1 );
innerPanelSouth.add( doTask2 ); 60
// set layout of this container and attach panels to it
setLayout( new BorderLayout() );
add( innerPanelCenter, BorderLayout.CENTER );
add( innerPanelSouth, BorderLayout.SOUTH ); 65
validate(); // validate layout 67
} // end constructor 69
// return reference to generic task button doTask1
public JButton getDoTask1Button() {
return doTask1; } 75
// return reference to generic task button doTask2
public JButton getDoTask2Button() {
return doTask2; }
BankUI.java Lines 73 and 79
Return the task buttons

20. BankUI.java 81 82 // return reference to fields array of JTextFields
public JTextField[] getFields() {
return fields; } 87
// clear content of text fields
public void clearFields() {
for ( int count = 0; count < size; count++ )
fields[ count ].setText( "" ); } 94
// set text field values; throw IllegalArgumentException if
// incorrect number of Strings in argument
public void setFieldValues( String strings[] )
throws IllegalArgumentException {
if ( strings.length != size )
throw new IllegalArgumentException( "There must be " +
size + " Strings in the array" );
103
for ( int count = 0; count < size; count++ )
fields[ count ].setText( strings[ count ] ); }
BankUI.java

21. 107
// get array of Strings with current text field contents
public String[] getFieldValues() {
String values[] = new String[ size ];
112
for ( int count = 0; count < size; count++ )
values[ count ] = fields[ count ].getText();
115
return values; }
118
119 } // end class BankUI
BankUI.java

22. AccountRecord.java Line 3 Line 7
// Fig. 17.6: AccountRecord.java
// A class that represents one record of information.
package com.deitel.jhtp5.ch17; 4
import java.io.Serializable; 6
public class AccountRecord implements Serializable {
private int account;
private String firstName;
private String lastName;
private double balance; 12
// no-argument constructor calls other constructor with default values
public AccountRecord() {
this( 0, "", "", 0.0 ); } 18
// initialize a record
public AccountRecord( int acct, String first, String last, double bal ) {
setAccount( acct );
setFirstName( first );
setLastName( last );
setBalance( bal ); } 27
Compile this class in a package for reuse
AccountRecord.java Line 3 Line 7
Implements Serializable so AccountRecords can be used with input and output streams

23. AccountRecord.java 28 // set account number
public void setAccount( int acct ) {
account = acct; } 33
// get account number
public int getAccount() {
return account; } 39
// set first name
public void setFirstName( String first ) {
firstName = first; } 45
// get first name
public String getFirstName() {
return firstName; } 51
AccountRecord.java

24. AccountRecord.java 52 // set last name
public void setLastName( String last ) {
lastName = last; } 57
// get last name
public String getLastName() {
return lastName; } 63
// set balance
public void setBalance( double bal ) {
balance = bal; } 69
// get balance
public double getBalance() {
return balance; } 75
76 } // end class AccountRecord
AccountRecord.java

25. CreateSequentialFile.java Lines 8-9 Lines 22 and 26
// Fig. 17.7: CreateSequentialFile.java
// Writing objects sequentially to a file with class ObjectOutputStream.
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*; 7
import com.deitel.jhtp5.ch17.BankUI;
import com.deitel.jhtp5.ch17.AccountRecord; 10
11 public class CreateSequentialFile extends JFrame {
private ObjectOutputStream output;
private BankUI userInterface;
private JButton enterButton, openButton; 15
// set up GUI
public CreateSequentialFile() {
super( "Creating a Sequential File of Objects" ); 20
// create instance of reusable user interface
userInterface = new BankUI( 4 ); // four textfields
getContentPane().add( userInterface, BorderLayout.CENTER ); 24
// configure button doTask1 for use in this program
openButton = userInterface.getDoTask1Button();
openButton.setText( "Save into File ..." );
CreateSequentialFile.java Lines 8-9 Lines 22 and 26
Import our GUI class and record class
Create our interface and get a reference to the first task button

26. CreateSequentialFile.java Line 4628
// register listener to call openFile when button pressed
openButton.addActionListener( 31
// anonymous inner class to handle openButton event
new ActionListener() { 34
// call openFile when button pressed
public void actionPerformed( ActionEvent event ) {
openFile(); } 40
} // end anonymous inner class 42
); // end call to addActionListener 44
// configure button doTask2 for use in this program
enterButton = userInterface.getDoTask2Button();
enterButton.setText( "Enter" );
enterButton.setEnabled( false ); // disable button 49
// register listener to call addRecord when button pressed
enterButton.addActionListener( 52
CreateSequentialFile.java Line 46
Get a reference to the second task button

27. 53 // anonymous inner class to handle enterButton event
new ActionListener() { 55
// call addRecord when button pressed
public void actionPerformed( ActionEvent event ) {
addRecord(); } 61
} // end anonymous inner class 63
); // end call to addActionListener 65
// register window listener to handle window closing event
addWindowListener( 68
// anonymous inner class to handle windowClosing event
new WindowAdapter() { 71
// add current record in GUI to file, then close file
public void windowClosing( WindowEvent event ) {
if ( output != null )
addRecord(); 77
closeFile(); }
CreateSequentialFile.java

28. Instantiate a JFileChooser and assign it to fileChooser80
} // end anonymous inner class 82
); // end call to addWindowListener 84
setSize( 300, 200 );
setVisible( true ); 87
} // end CreateSequentialFile constructor 89
// allow user to specify file name
private void openFile() {
// display file dialog, so user can choose file to open
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY ); 96
int result = fileChooser.showSaveDialog( this ); 98
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
102
File fileName = fileChooser.getSelectedFile(); // get selected file
104
CreateSequentialFile.java Line 94 Line 95 Line 97 Lines Line 103
Instantiate a JFileChooser and assign it to fileChooser
Constant FILES_ONLY indicates only files can be selected
Method showSaveDialog causes the JFileChooser titled Save to appear
Return if user clicked Cancel button on dialog
Retrieve selected file

29. CreateSequentialFile.java Open selected file
// display error if invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
109
else {
111
// open file
try {
output = new ObjectOutputStream(
new FileOutputStream( fileName ) );
116
openButton.setEnabled( false );
enterButton.setEnabled( true ); }
120
// process exceptions from opening file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error Opening File",
"Error", JOptionPane.ERROR_MESSAGE ); }
126
} // end else
128
} // end method openFile
130
CreateSequentialFile.java
Open selected file

30. CreateSequentialFile.java Line 132 Line 154
// close file and terminate application
private void closeFile() {
// close file
try {
output.close();
System.exit( 0 ); }
139
// process exceptions from closing file
catch( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error closing file",
"Error", JOptionPane.ERROR_MESSAGE );
System.exit( 1 ); }
146
} // end method closeFile
148
// add record to file
public void addRecord() {
int accountNumber = 0;
AccountRecord record;
String fieldValues[] = userInterface.getFieldValues();
155
Method closeFile closes the current file
CreateSequentialFile.java Line 132 Line 154
Get the data in the textfields

31. CreateSequentialFile.java Lines 167-170 Lines 173-174
// if account field value is not empty
if ( ! fieldValues[ BankUI.ACCOUNT ].equals( "" ) ) {
158
// output values to file
try {
accountNumber = Integer.parseInt(
fieldValues[ BankUI.ACCOUNT ] );
163
if ( accountNumber > 0 ) {
165
// create new record
record = new AccountRecord( accountNumber,
fieldValues[ BankUI.FIRSTNAME ],
fieldValues[ BankUI.LASTNAME ],
Double.parseDouble( fieldValues[ BankUI.BALANCE ] ) );
171
// output record and flush buffer
output.writeObject( record );
output.flush(); }
176
else {
JOptionPane.showMessageDialog( this,
"Account number must be greater than 0",
"Bad account number", JOptionPane.ERROR_MESSAGE ); }
182
CreateSequentialFile.java Lines Lines
Create a new record
Write the record to the file immediately

32. CreateSequentialFile.java 183 // clear textfields
userInterface.clearFields();
185
} // end try
187
// process invalid account number or balance format
catch ( NumberFormatException formatException ) {
JOptionPane.showMessageDialog( this,
"Bad account number or balance", "Invalid Number Format",
JOptionPane.ERROR_MESSAGE ); }
194
// process exceptions from file output
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error writing to file",
"IO Exception", JOptionPane.ERROR_MESSAGE );
closeFile(); }
201
} // end if
203
} // end method addRecord
205
CreateSequentialFile.java

33. CreateSequentialFile.java 206 public static void main( String args[] ){
new CreateSequentialFile(); }
210
211 } // end class CreateSequentialFile
CreateSequentialFile.java
BankUI graphical user interface

34. CreateSequentialFile.java Select location for file here
Files and directories are displayed here
Click Save to submit new file name to program

35. 17.6 Reading Data from a Sequential-Access File
Data stored in files
Retrieved for processing when needed
Accessing a sequential file
Data must be read in same format it was written

36. Fig. 17.8 Sample data for the program of Fig. 17.7

37. ReadSequentialFile.java Line 22
// Fig. 17.9: ReadSequentialFile.java
// This program reads a file of objects sequentially
// and displays each record.
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*; 8
import com.deitel.jhtp5.ch17.*; 10
11 public class ReadSequentialFile extends JFrame {
private ObjectInputStream input;
private BankUI userInterface;
private JButton nextButton, openButton; 15
// Constructor -- initialize the Frame
public ReadSequentialFile() {
super( "Reading a Sequential File of Objects" ); 20
// create instance of reusable user interface
userInterface = new BankUI( 4 ); // four textfields
getContentPane().add( userInterface, BorderLayout.CENTER ); 24
ReadSequentialFile.java Line 22
Create user interface

38. ReadSequentialFile.java Line 27
// get reference to generic task button doTask1 from BankUI
openButton = userInterface.getDoTask1Button();
openButton.setText( "Open File" ); 28
// register listener to call openFile when button pressed
openButton.addActionListener( 31
// anonymous inner class to handle openButton event
new ActionListener() { 34
// close file and terminate application
public void actionPerformed( ActionEvent event ) {
openFile(); } 40
} // end anonymous inner class 42
); // end call to addActionListener 44
// register window listener for window closing event
addWindowListener( 47
// anonymous inner class to handle windowClosing event
new WindowAdapter() { 50
Get a reference to the first task button
ReadSequentialFile.java Line 27

39. ReadSequentialFile.java Line 65
// close file and terminate application
public void windowClosing( WindowEvent event ) {
if ( input != null )
closeFile(); 56
System.exit( 0 ); } 59
} // end anonymous inner class 61
); // end call to addWindowListener 63
// get reference to generic task button doTask2 from BankUI
nextButton = userInterface.getDoTask2Button();
nextButton.setText( "Next Record" );
nextButton.setEnabled( false ); 68
// register listener to call readRecord when button pressed
nextButton.addActionListener( 71
// anonymous inner class to handle nextRecord event
new ActionListener() { 74
ReadSequentialFile.java Line 65
Get a reference to the second task button

40. ReadSequentialFile.java Line 95 Line 96 Line 98
// call readRecord when user clicks nextRecord
public void actionPerformed( ActionEvent event ) {
readRecord(); } 80
} // end anonymous inner class 82
); // end call to addActionListener 84
pack();
setSize( 300, 200 );
setVisible( true ); 88
} // end ReadSequentialFile constructor 90
// enable user to select file to open
private void openFile() {
// display file dialog so user can select file to open
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY ); 97
int result = fileChooser.showOpenDialog( this ); 99
ReadSequentialFile.java Line 95 Line 96 Line 98
Instantiate a JFileChooser and assign it to fileChooser
Constant FILES_ONLY indicates only files can be selected
Method showOpenDialog causes the JFileChooser titled Open to appear

41. ReadSequentialFile.java Line 101-102 Line 105 Lines 116-117
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
103
// obtain selected file
File fileName = fileChooser.getSelectedFile();
106
// display error if file name invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
111
else {
113
// open file
try {
input = new ObjectInputStream(
new FileInputStream( fileName ) );
118
openButton.setEnabled( false );
nextButton.setEnabled( true ); }
122
// process exceptions opening file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error Opening File",
"Error", JOptionPane.ERROR_MESSAGE ); }
Return if user clicked Cancel button on dialog
ReadSequentialFile.java Line Line 105 Lines
Retrieve selected file
Open selected file

42. ReadSequentialFile.java Line 140
128
} // end else
130
} // end method openFile
132
// read record from file
public void readRecord() {
AccountRecord record;
137
// input the values from the file
try {
record = ( AccountRecord ) input.readObject();
141
// create array of Strings to display in GUI
String values[] = { String.valueOf( record.getAccount() ),
record.getFirstName(), record.getLastName(),
String.valueOf( record.getBalance() ) };
146
// display record contents
userInterface.setFieldValues( values ); }
150
// display message when end-of-file reached
catch ( EOFException endOfFileException ) {
nextButton.setEnabled( false );
154
ReadSequentialFile.java Line 140
Method readObject reads an Object from the ObjectInputStream

43. ReadSequentialFile.java Line 175
JOptionPane.showMessageDialog( this, "No more records in file",
"End of File", JOptionPane.ERROR_MESSAGE ); }
158
// display error message if class is not found
catch ( ClassNotFoundException classNotFoundException ) {
JOptionPane.showMessageDialog( this, "Unable to create object",
"Class Not Found", JOptionPane.ERROR_MESSAGE ); }
164
// display error message if cannot read due to problem with file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this,
"Error during read from file",
"Read Error", JOptionPane.ERROR_MESSAGE ); }
171
} // end method readRecord
173
// close file and terminate application
private void closeFile() {
// close file and exit
try {
input.close();
System.exit( 0 ); }
ReadSequentialFile.java Line 175
Method closeFile closes the current file

44. ReadSequentialFile.java 182
// process exception while closing file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error closing file",
"Error", JOptionPane.ERROR_MESSAGE );
187
System.exit( 1 ); }
190
} // end method closeFile
192
public static void main( String args[] ) {
new ReadSequentialFile(); }
197
198 } // end class ReadSequentialFile
ReadSequentialFile.java

45. ReadSequentialFile.java

46. CreditInquiry.java 1 // Fig. 17.10: CreditInquiry.java
// This program reads a file sequentially and displays the contents in a
// text area based on the type of account the user requests
// (credit balance, debit balance or zero balance).
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;
import javax.swing.*; 10
11 import com.deitel.jhtp5.ch17.AccountRecord; 12
13 public class CreditInquiry extends JFrame {
private JTextArea recordDisplayArea;
private JButton openButton, creditButton, debitButton, zeroButton;
private JPanel buttonPanel; 17
private ObjectInputStream input;
private FileInputStream fileInput;
private File fileName;
private String accountType; 22
static private DecimalFormat twoDigits = new DecimalFormat( "0.00" ); 24
// set up GUI
public CreditInquiry() {
CreditInquiry.java

47. CreditInquiry.java 28 super( "Credit Inquiry Program" ); 29
Container container = getContentPane(); 31
buttonPanel = new JPanel(); // set up panel for buttons 33
// create and configure button to open file
openButton = new JButton( "Open File" );
buttonPanel.add( openButton ); 37
// register openButton listener
openButton.addActionListener( 40
// anonymous inner class to handle openButton event
new ActionListener() { 43
// open file for processing
public void actionPerformed( ActionEvent event ) {
openFile(); } 49
} // end anonymous inner class 51
); // end call to addActionListener
CreditInquiry.java

48. 53
// create and configure button to get accounts with credit balances
creditButton = new JButton( "Credit balances" );
buttonPanel.add( creditButton );
creditButton.addActionListener( new ButtonHandler() ); 58
// create and configure button to get accounts with debit balances
debitButton = new JButton( "Debit balances" );
buttonPanel.add( debitButton );
debitButton.addActionListener( new ButtonHandler() ); 63
// create and configure button to get accounts with zero balances
zeroButton = new JButton( "Zero balances" );
buttonPanel.add( zeroButton );
zeroButton.addActionListener( new ButtonHandler() ); 68
// set up display area
recordDisplayArea = new JTextArea();
JScrollPane scroller = new JScrollPane( recordDisplayArea ); 72
// attach components to content pane
container.add( scroller, BorderLayout.CENTER );
container.add( buttonPanel, BorderLayout.SOUTH ); 76
CreditInquiry.java

49. 77 creditButton.setEnabled( false ); // disable creditButton
debitButton.setEnabled( false ); // disable debitButton
zeroButton.setEnabled( false ); // disable zeroButton 80
// register window listener
addWindowListener( 83
// anonymous inner class for windowClosing event
new WindowAdapter() { 86
// close file and terminate program
public void windowClosing( WindowEvent event ) {
closeFile();
System.exit( 0 ); } 93
} // end anonymous inner class 95
); // end call to addWindowListener 97
pack(); // pack components and display window
setSize( 600, 250 );
setVisible( true );
101
} // end CreditInquiry constructor
103
CreditInquiry.java

50. CreditInquiry.java 104 // enable user to choose file to open
private void openFile() {
// display dialog, so user can choose file
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY );
110
int result = fileChooser.showOpenDialog( this );
112
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
116
fileName = fileChooser.getSelectedFile(); // obtain selected file
118
// display error if file name invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
123
// open file
try {
126
// close file from previous operation
if ( input != null )
input.close();
130
CreditInquiry.java

51. CreditInquiry.java 131 fileInput = new FileInputStream( fileName );
input = new ObjectInputStream( fileInput );
openButton.setEnabled( false );
creditButton.setEnabled( true );
debitButton.setEnabled( true );
zeroButton.setEnabled( true ); }
138
// catch problems manipulating file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "File does not exist",
"Invalid File Name", JOptionPane.ERROR_MESSAGE ); }
144
} // end method openFile
146
// close file before application terminates
private void closeFile() {
// close file
try {
if ( input != null )
input.close(); }
155
CreditInquiry.java

52. CreditInquiry.java Lines 177-178
// process exception from closing file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error closing file",
"Error", JOptionPane.ERROR_MESSAGE );
160
System.exit( 1 ); }
163
} // end method closeFile
165
// read records from file and display only records of appropriate type
private void readRecords() {
AccountRecord record;
170
// read records
try {
173
if ( input != null )
input.close();
176
fileInput = new FileInputStream( fileName );
input = new ObjectInputStream( fileInput );
179
recordDisplayArea.setText( "The accounts are:\n" );
181
CreditInquiry.java Lines
Create a stream from which to read the records

53. CreditInquiry.java Line 186 Line 198
// input the values from the file
while ( true ) {
184
// read one AccountRecord
record = ( AccountRecord ) input.readObject();
187
// if proper acount type, display record
if ( shouldDisplay( record.getBalance() ) )
recordDisplayArea.append( record.getAccount() + "\t" +
record.getFirstName() + "\t" + record.getLastName() +
"\t" + twoDigits.format( record.getBalance() ) + "\n" ); }
194
} // end try
196
// close file when end-of-file reached
catch ( EOFException eofException ) {
closeFile(); }
201
// display error if cannot read object because class not found
catch ( ClassNotFoundException classNotFound ) {
JOptionPane.showMessageDialog( this, "Unable to create object",
"Class Not Found", JOptionPane.ERROR_MESSAGE ); }
Method readObject reads an Object from the ObjectInputStream
CreditInquiry.java Line 186 Line 198
An EOFException is thrown when the end of the file is reached

54. 207
// display error if cannot read because problem with file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error reading from file",
"Error", JOptionPane.ERROR_MESSAGE ); }
213
} // end method readRecords
215
// use record type to determine if record should be displayed
private boolean shouldDisplay( double balance ) {
if ( accountType.equals( "Credit balances" ) && balance < 0 )
return true;
221
else if ( accountType.equals( "Debit balances" ) && balance > 0 )
return true;
224
else if ( accountType.equals( "Zero balances" ) && balance == 0 )
return true;
227
return false; }
230
CreditInquiry.java

55. CreditInquiry.java 231 public static void main( String args[] ) 232 {{
new CreditInquiry(); }
235
// class for creditButton, debitButton and zeroButton event handling
private class ButtonHandler implements ActionListener {
238
// read records from file
public void actionPerformed( ActionEvent event ) {
accountType = event.getActionCommand();
readRecords(); }
245
} // end class ButtonHandler
247
248 } // end class CreditInquiry
CreditInquiry.java

56. CreditInquiry.java

57. 17.7 Updating Sequential-Access Files
Difficult to update a sequential-access file
Entire file must be rewritten to change one field
Only acceptable if many records being updated at once

58. “Instant-access” applications
17.8 Random-Access Files
“Instant-access” applications
Record must be located immediately
Transaction-processing systems require rapid access
Random-access files
Access individual records directly and quickly
Use fixed length for every record
Easy to calculate record locations
Insert records without destroying other data in file
Fig shows random-access file

59. Fig. 17.11 Java’s view of a random-access file
100
bytes
200
300
400
500
byte offsets

60. 17.9 Creating a Random-Access File
RandomAccessFile objects
Like DataInputStream and DataOutputstream
Reads or writes data in spot specified by file-position pointer
Manipulates all data as primitive types
Normally writes one object at a time to file

61. RandomAccessAccountRecord.java Line 7
// Fig : RandomAccessAccountRecord.java
// Subclass of AccountRecord for random access file programs.
package com.deitel.jhtp5.ch17; 4
import java.io.*; 6
public class RandomAccessAccountRecord extends AccountRecord { 8
public static final int SIZE = 72; // bytes in one record 10
// no-argument constructor calls other constructor with default values
public RandomAccessAccountRecord() {
this( 0, "", "", 0.0 ); } 16
// initialize a RandomAccessAccountRecord
public RandomAccessAccountRecord( int account, String firstName,
String lastName, double balance ) {
super( account, firstName, lastName, balance ); } 23
Class extends AccountRecord
RandomAccessAccountRecord.java Line 7

62. RandomAccessAccountRecord.java Line 25 Line 27 Line 30 Line 39
// read a record from specified RandomAccessFile
public void read( RandomAccessFile file ) throws IOException {
setAccount( file.readInt() );
setFirstName( readName( file ) );
setLastName( readName( file ) );
setBalance( file.readDouble() ); } 32
// ensure that name is proper length
private String readName( RandomAccessFile file ) throws IOException {
char name[] = new char[ 15 ], temp; 37
for ( int count = 0; count < name.length; count++ ) {
temp = file.readChar();
name[ count ] = temp; } 42
return new String( name ).replace( '\0', ' ' ); } 45
Method read reads one record from the RandomAccessFile
RandomAccessAccountRecord.java Line 25 Line 27 Line 30 Line 39
Method readInt reads one integer
Method readDouble reads one double
Method readChar reads one character

63. RandomAccessAccountRecord.java Line 47 Line 49 Line 52 Line 56 Line 67
// write a record to specified RandomAccessFile
public void write( RandomAccessFile file ) throws IOException {
file.writeInt( getAccount() );
writeName( file, getFirstName() );
writeName( file, getLastName() );
file.writeDouble( getBalance() ); } 54
// write a name to file; maximum of 15 characters
private void writeName( RandomAccessFile file, String name )
throws IOException {
StringBuffer buffer = null; 60
if ( name != null )
buffer = new StringBuffer( name );
else
buffer = new StringBuffer( 15 ); 65
buffer.setLength( 15 );
file.writeChars( buffer.toString() ); } 69
70 } // end class RandomAccessAccountRecord
Method write writes one record to the RandomAccessFile
RandomAccessAccountRecord.java Line 47 Line 49 Line 52 Line 56 Line 67
Method writeInt writes one integer
Method writeDouble writes one double
Method writeName writes a string to the file
Method writeChars writes a string

64. CreateRandomFile.java 1 // Fig. 17.13: CreateRandomFile.java
// Creates random access file by writing 100 empty records to disk.
import java.io.*;
import javax.swing.*; 5
import com.deitel.jhtp5.ch17.RandomAccessAccountRecord; 7
public class CreateRandomFile { 9
private static final int NUMBER_RECORDS = 100; 11
// enable user to select file to open
private void createFile() {
// display dialog so user can choose file
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY ); 18
int result = fileChooser.showSaveDialog( null ); 20
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return; 24
// obtain selected file
File fileName = fileChooser.getSelectedFile();
CreateRandomFile.java

65. CreateRandomFile.java Lines 37-38 Line 4527
// display error if file name invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( null, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE ); 32
else { 34
// open file
try {
RandomAccessFile file =
new RandomAccessFile( fileName, "rw" ); 39
RandomAccessAccountRecord blankRecord =
new RandomAccessAccountRecord(); 42
// write 100 blank records
for ( int count = 0; count < NUMBER_RECORDS; count++ )
blankRecord.write( file ); 46
file.close(); // close file 48
// display message that file was created
JOptionPane.showMessageDialog( null, "Created file " +
fileName, "Status", JOptionPane.INFORMATION_MESSAGE );
CreateRandomFile.java Lines Line 45
Open a RandomAccessFile
Write 100 blank records

66. CreateRandomFile.java 52 53 System.exit( 0 ); // terminate program 54
} // end try 56
// process exceptions during open, write or close file operations
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( null, "Error processing file",
"Error processing file", JOptionPane.ERROR_MESSAGE ); 61
System.exit( 1 ); } 64
} // end else 66
} // end method createFile 68
public static void main( String args[] ) {
CreateRandomFile application = new CreateRandomFile();
application.createFile(); } 74
75 } // end class CreateRandomFile
CreateRandomFile.java

67. CreateRandomFile.java

68. 17.10 Writing Data Randomly to a Random-Access File
RandomAccessFile method seek
Determines location in file where record is stored
Sets file-position pointer to a specific point in file

69. WriteRandomFile.java 1 // Fig. 17.14: WriteRandomFile.java
// This program uses textfields to get information from the user at the
// keyboard and writes the information to a random-access file.
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*; 8
import com.deitel.jhtp5.ch17.*; 10
11 public class WriteRandomFile extends JFrame {
private RandomAccessFile output;
private BankUI userInterface;
private JButton enterButton, openButton; 15
private static final int NUMBER_RECORDS = 100; 17
// set up GUI
public WriteRandomFile() {
super( "Write to random access file" ); 22
// create instance of reusable user interface BankUI
userInterface = new BankUI( 4 ); // four textfields
getContentPane().add( userInterface,
BorderLayout.CENTER );
WriteRandomFile.java

70. 27
// get reference to generic task button doTask1 in BankUI
openButton = userInterface.getDoTask1Button();
openButton.setText( "Open..." ); 31
// register listener to call openFile when button pressed
openButton.addActionListener( 34
// anonymous inner class to handle openButton event
new ActionListener() { 37
// allow user to select file to open
public void actionPerformed( ActionEvent event ) {
openFile(); } 43
} // end anonymous inner class 45
); // end call to addActionListener 47
// register window listener for window closing event
addWindowListener( 50
WriteRandomFile.java

71. 51 // anonymous inner class to handle windowClosing event
new WindowAdapter() { 53
// add record in GUI, then close file
public void windowClosing( WindowEvent event ) {
if ( output != null )
addRecord(); 59
closeFile(); } 62
} // end anonymous inner class 64
); // end call to addWindowListener 66
// get reference to generic task button doTask2 in BankUI
enterButton = userInterface.getDoTask2Button();
enterButton.setText( "Enter" );
enterButton.setEnabled( false ); 71
// register listener to call addRecord when button pressed
enterButton.addActionListener( 74
WriteRandomFile.java

72. 75 // anonymous inner class to handle enterButton event
new ActionListener() { 77
// add record to file
public void actionPerformed( ActionEvent event ) {
addRecord(); } 83
} // end anonymous inner class 85
); // end call to addActionListener 87
setSize( 300, 150 );
setVisible( true ); } 91
// enable user to choose file to open
private void openFile() {
// display file dialog so user can select file
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY ); 98
int result = fileChooser.showOpenDialog( this );
100
WriteRandomFile.java

73. WriteRandomFile.java Line 117
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
104
// obtain selected file
File fileName = fileChooser.getSelectedFile();
107
// display error if file name invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
112
else {
114
// open file
try {
output = new RandomAccessFile( fileName, "rw" );
enterButton.setEnabled( true );
openButton.setEnabled( false ); }
121
// process exception while opening file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "File does not exist",
"Invalid File Name", JOptionPane.ERROR_MESSAGE ); }
WriteRandomFile.java Line 117
Open a RandomAccessFile

74. WriteRandomFile.java 127 128 } // end else 129
} // end method openFile
131
// close file and terminate application
private void closeFile() {
// close file and exit
try {
if ( output != null )
output.close();
139
System.exit( 0 ); }
142
// process exception while closing file
catch( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error closing file",
"Error", JOptionPane.ERROR_MESSAGE );
147
System.exit( 1 ); }
150
} // end method closeFile
152
WriteRandomFile.java

75. WriteRandomFile.java Lines 176-177
// add one record to file
private void addRecord() {
String fields[] = userInterface.getFieldValues();
157
// ensure account field has a value
if ( ! fields[ BankUI.ACCOUNT ].equals( "" ) ) {
160
// output values to file
try {
int accountNumber =
Integer.parseInt( fields[ ACCOUNT ] );
165
if ( accountNumber > 0 && accountNumber <= NUMBER_RECORDS ) {
RandomAccessAccountRecord record
new RandomAccessAccountRecord();
169
record.setAccount( accountNumber );
record.setFirstName( fields[ BankUI.FIRSTNAME ] );
record.setLastName( fields[ BankUI.LASTNAME ] );
record.setBalance( Double.parseDouble(
fields[ BankUI.BALANCE ] ) );
175
output.seek( ( accountNumber - 1 ) *
RandomAccessAccountRecord.SIZE );
record.write( output ); }
WriteRandomFile.java Lines
Set the file pointer to the appropriate place

76. WriteRandomFile.java 180 181 else {
JOptionPane.showMessageDialog( this,
"Account must be between 1 and 100",
"Invalid account number", JOptionPane.ERROR_MESSAGE ); }
186
userInterface.clearFields(); // clear TextFields
188
} // end try
190
// process improper account number or balance format
catch ( NumberFormatException formatException ) {
JOptionPane.showMessageDialog( this,
"Bad account number or balance",
"Invalid Number Format", JOptionPane.ERROR_MESSAGE ); }
197
// process exceptions while writing to file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this,
"Error writing to the file", "IO Exception",
JOptionPane.ERROR_MESSAGE );
closeFile(); }
WriteRandomFile.java

77. WriteRandomFile.java 205 206 } // end if 207
} // end method addRecord
209
public static void main( String args[] ) {
new WriteRandomFile(); }
214
215 } // end class WriteRandomFile
WriteRandomFile.java

78. WriteRandomFile.java

79. 17.11 Reading Data Sequentially from a Random-Access File
Read all valid records in a RandomAccessFile

80. ReadRandomFile.java 1 // Fig. 17.15: ReadRandomFile.java
// This program reads a random-access file sequentially and
// displays the contents one record at a time in text fields.
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.text.DecimalFormat;
import javax.swing.*; 9
10 import com.deitel.jhtp5.ch17.*; 11
12 public class ReadRandomFile extends JFrame {
private BankUI userInterface;
private RandomAccessFile input;
private JButton nextButton, openButton; 16
private static DecimalFormat twoDigits = new DecimalFormat( "0.00" ); 18
// set up GUI
public ReadRandomFile() {
super( "Read Client File" ); 23
// create reusable user interface instance
userInterface = new BankUI( 4 ); // four textfields
getContentPane().add( userInterface );
ReadRandomFile.java

81. 27
// configure generic doTask1 button from BankUI
openButton = userInterface.getDoTask1Button();
openButton.setText( "Open File for Reading..." ); 31
// register listener to call openFile when button pressed
openButton.addActionListener( 34
// anonymous inner class to handle openButton event
new ActionListener() { 37
// enable user to select file to open
public void actionPerformed( ActionEvent event ) {
openFile(); } 43
} // end anonymous inner class 45
); // end call to addActionListener 47
// configure generic doTask2 button from BankUI
nextButton = userInterface.getDoTask2Button();
nextButton.setText( "Next" );
nextButton.setEnabled( false );
ReadRandomFile.java

82. 52
// register listener to call readRecord when button pressed
nextButton.addActionListener( 55
// anonymous inner class to handle nextButton event
new ActionListener() { 58
// read a record when user clicks nextButton
public void actionPerformed( ActionEvent event ) {
readRecord(); } 64
} // end anonymous inner class 66
); // end call to addActionListener 68
// register listener for window closing event
addWindowListener( 71
// anonymous inner class to handle windowClosing event
new WindowAdapter() { 74
ReadRandomFile.java

83. ReadRandomFile.java 75 // close file and terminate application
public void windowClosing( WindowEvent event ) {
closeFile(); } 80
} // end anonymous inner class 82
); // end call to addWindowListener 84
setSize( 300, 150 );
setVisible( true ); 87
} // end constructor 89
// enable user to select file to open
private void openFile() {
// display file dialog so user can select file
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY ); 96
int result = fileChooser.showOpenDialog( this ); 98
ReadRandomFile.java

84. ReadRandomFile.java Line 115
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
102
// obtain selected file
File fileName = fileChooser.getSelectedFile();
105
// display error is file name invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
110
else {
112
// open file
try {
input = new RandomAccessFile( fileName, "r" );
nextButton.setEnabled( true );
openButton.setEnabled( false ); }
119
// catch exception while opening file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "File does not exist",
"Invalid File Name", JOptionPane.ERROR_MESSAGE ); }
ReadRandomFile.java Line 115
Open a RandomAccessFile

85. ReadRandomFile.java Line 139
125
} // end else
127
} // end method openFile
129
// read one record
private void readRecord() {
RandomAccessAccountRecord record = new RandomAccessAccountRecord();
134
// read a record and display
try {
137
do {
record.read( input );
} while ( record.getAccount() == 0 );
141
String values[] = { String.valueOf( record.getAccount() ),
record.getFirstName(), record.getLastName(),
String.valueOf( record.getBalance() ) };
userInterface.setFieldValues( values ); }
147
ReadRandomFile.java Line 139
Read until a valid record is found

86. ReadRandomFile.java Line 149
// close file when end-of-file reached
catch ( EOFException eofException ) {
JOptionPane.showMessageDialog( this, "No more records",
"End-of-file reached", JOptionPane.INFORMATION_MESSAGE );
closeFile(); }
154
// process exceptions from problem with file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error Reading File",
"Error", JOptionPane.ERROR_MESSAGE );
159
System.exit( 1 ); }
162
} // end method readRecord
164
// close file and terminate application
private void closeFile() {
// close file and exit
try {
if ( input != null )
input.close();
172
System.exit( 0 ); }
If the end-of-file marker is reached, there are no more records
ReadRandomFile.java Line 149

87. ReadRandomFile.java 175 176 // process exception closing file
catch( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error closing file",
"Error", JOptionPane.ERROR_MESSAGE );
180
System.exit( 1 ); }
183
} // end method closeFile
185
public static void main( String args[] ) {
new ReadRandomFile(); }
190
191 } // end class ReadRandomFile
ReadRandomFile.java

88. ReadRandomFile.java

89. 17.12 Case Study: A Transaction-Processing Program
Substantial transaction-processing system
Uses random-access file
Updates, adds and deletes accounts

90. Fig. 17.16 Transaction Processor window

91. Fig. 17.17 Update Record: Loading a record to update
Type account number and press the Enter key to load record.
Action button has a different label depending on the operation to perform.

92. Fig. 17.18 Update Record: Inputting a transaction
Updated balance after user pressed Update.
Enter transaction amount.

93. Fig. 17.19 New Record: Adding a record to the file

94. Fig. 17.20 Delete Record: Removing a record from the file

95. TransactionProcessor.java 1 // Fig. 17.21: TransactionProcessor.java
// A transaction processing program using random-access files.
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.text.DecimalFormat;
import javax.swing.*; 8
import com.deitel.jhtp5.ch17.*; 10
11 public class TransactionProcessor extends JFrame { 12
private BankUI userInterface;
private JMenuItem newItem, updateItem, deleteItem, openItem, exitItem;
private JTextField fields[];
private JTextField accountField, transactionField;
private JButton actionButton, cancelButton;
private FileEditor dataFile;
private RandomAccessAccountRecord record; 20
public TransactionProcessor() {
super( "Transaction Processor" ); 24
TransactionProcessor.java

96. TransactionProcessor.java 25 // set up desktop, menu bar and File menu
userInterface = new BankUI( 5 );
getContentPane().add( userInterface );
userInterface.setVisible( false ); 29
// set up the action button
actionButton = userInterface.getDoTask1Button();
actionButton.setText( "Save Changes" );
actionButton.setEnabled( false ); 34
// register action button listener
actionButton.addActionListener( 37
new ActionListener() { // anonymous inner class 39
public void actionPerformed( ActionEvent event ) {
String action = event.getActionCommand();
performAction( action ); 44
} // end method actionPerformed 46
} // end anonymous inner class 48
); // end call to addActionListener 50
TransactionProcessor.java

97. TransactionProcessor.java 51 // set up the cancel button
cancelButton = userInterface.getDoTask2Button();
cancelButton.setText( "Cancel" );
cancelButton.setEnabled( false ); 55
// register cancel button listener
cancelButton.addActionListener( 58
new ActionListener() { // anonymous inner class 60
// clear the fields
public void actionPerformed( ActionEvent event ) {
userInterface.clearFields(); } 66
} // end anonymous inner class 68
); // end call to addActionListener 70
// set up the listener for the account field
fields = userInterface.getFields();
accountField = fields[ BankUI.ACCOUNT ];
accountField.addActionListener( 75
TransactionProcessor.java

98. 76 new ActionListener() { // anonymous inner class77
public void actionPerformed( ActionEvent event ) {
displayRecord( "0" ); } 82
} // end anonymous inner class 84
); // end call to addActionListener 86
// create reference to the transaction field
transactionField = fields[ BankUI.TRANSACTION ]; 89
// register transaction field listener
transactionField.addActionListener( 92
new ActionListener() { // anonymous inner class 94
// update the GUI fields
public void actionPerformed( ActionEvent event ) {
displayRecord( transactionField.getText() ); }
100
} // end anonymous inner class
102
TransactionProcessor.java

99. TransactionProcessor.java 103 ); // end call to addActionListener 104
JMenuBar menuBar = new JMenuBar(); // set up the menu
setJMenuBar( menuBar );
107
JMenu fileMenu = new JMenu( "File" );
menuBar.add( fileMenu );
110
// set up menu item for adding a record
newItem = new JMenuItem( "New Record" );
newItem.setEnabled( false );
114
// register new item listener
newItem.addActionListener(
117
new ActionListener() { // anonymous inner class
119
public void actionPerformed( ActionEvent event ) {
122
// set up the GUI fields for editing
fields[ BankUI.ACCOUNT ].setEnabled( true );
fields[ BankUI.FIRSTNAME ].setEnabled( true );
fields[ BankUI.LASTNAME ].setEnabled( true );
fields[ BankUI.BALANCE ].setEnabled( true );
fields[ BankUI.TRANSACTION ].setEnabled( false );
TransactionProcessor.java

100. TransactionProcessor.java 129 130 actionButton.setEnabled( true );
actionButton.setText( "Create" );
cancelButton.setEnabled( true );
133
userInterface.clearFields(); // reset the textfields
135
} // end method actionPerformed
137
} // end anonymous inner class
139
); // end call to addActionListener
141
// set up menu item for updating a record
updateItem = new JMenuItem( "Update Record" );
updateItem.setEnabled( false );
145
// register update item listener
updateItem.addActionListener(
148
new ActionListener() { // anonymous inner class
150
public void actionPerformed( ActionEvent event ) {
TransactionProcessor.java

101. TransactionProcessor.java 153 // set up the GUI fields for editing
fields[ BankUI.ACCOUNT ].setEnabled( true );
fields[ BankUI.FIRSTNAME ].setEnabled( false );
fields[ BankUI.LASTNAME ].setEnabled( false );
fields[ BankUI.BALANCE ].setEnabled( false );
fields[ BankUI.TRANSACTION ].setEnabled( true );
159
actionButton.setEnabled( true );
actionButton.setText( "Update" );
cancelButton.setEnabled( true );
163
userInterface.clearFields(); // reset the textfields
165
} // end method actionPerformed
167
} // end anonymous inner class
169
); // end call to addActionListener
171
// set up menu item for deleting a record
deleteItem = new JMenuItem( "Delete Record" );
deleteItem.setEnabled( false );
175
// register delete item listener
deleteItem.addActionListener(
178
TransactionProcessor.java

102. 179 new ActionListener() { // anonymous inner class
180
public void actionPerformed( ActionEvent event ) {
// set up the GUI fields for editing
fields[ BankUI.ACCOUNT ].setEnabled( true );
fields[ BankUI.FIRSTNAME ].setEnabled( false );
fields[ BankUI.LASTNAME ].setEnabled( false );
fields[ BankUI.BALANCE ].setEnabled( false );
fields[ BankUI.TRANSACTION ].setEnabled( false );
189
actionButton.setEnabled( true );
actionButton.setText( "Delete" );
cancelButton.setEnabled( true );
193
userInterface.clearFields(); // reset the textfields
195
} // end method actionPerformed
197
} // end anonymous inner class
199
); // end call to addActionListener
201
// set up menu item for opening file
openItem = new JMenuItem( "New/Open File" );
204
TransactionProcessor.java

103. TransactionProcessor.java 205 // register open item listener
openItem.addActionListener(
207
new ActionListener() { // anonymous inner class
209
public void actionPerformed( ActionEvent event ) {
// try to open the file
if ( !openFile() )
return;
215
// set up the menu items
newItem.setEnabled( true );
updateItem.setEnabled( true );
deleteItem.setEnabled( true );
openItem.setEnabled( false );
221
// set the interface
userInterface.setVisible( true );
fields[ BankUI.ACCOUNT ].setEnabled( false );
fields[ BankUI.FIRSTNAME ].setEnabled( false );
fields[ BankUI.LASTNAME ].setEnabled( false );
fields[ BankUI.BALANCE ].setEnabled( false );
fields[ BankUI.TRANSACTION ].setEnabled( false );
229
} // end method actionPerformed
231
TransactionProcessor.java

104. TransactionProcessor.java 232 } // end anonymous inner class 233
); // end call to addActionListener
235
// set up menu item for exiting program
exitItem = new JMenuItem( "Exit" );
238
// register exit item listener
exitItem.addActionListener(
241
new ActionListener() { // anonyomus inner class
243
public void actionPerformed( ActionEvent event ) {
try {
dataFile.closeFile(); // close the file }
249
catch ( IOException ioException ) {
JOptionPane.showMessageDialog(
TransactionProcessor.this, "Error closing file",
"IO Error", JOptionPane.ERROR_MESSAGE ); }
255
finally {
System.exit( 0 ); // exit the program }
TransactionProcessor.java

105. TransactionProcessor.java 259 260 } // end method actionPerformed 261
} // end anonymous inner class
263
); // end call to addActionListener
265
// attach menu items to File menu
fileMenu.add( openItem );
fileMenu.add( newItem );
fileMenu.add( updateItem );
fileMenu.add( deleteItem );
fileMenu.addSeparator();
fileMenu.add( exitItem );
273
setSize( 400, 250 );
setVisible( true );
276
} // end constructor
278
public static void main( String args[] ) {
new TransactionProcessor(); }
283
TransactionProcessor.java

106. TransactionProcessor.java Line 309
// get the file name and open the file
private boolean openFile() {
// display dialog so user can select file
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY );
290
int result = fileChooser.showOpenDialog( this );
292
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return false;
296
// obtain selected file
File fileName = fileChooser.getSelectedFile();
299
// display error if file name invalid
if ( fileName == null || fileName.getName().equals( "" ) ) {
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Bad File Name", JOptionPane.ERROR_MESSAGE );
return false; }
306
try {
// call the helper method to open the file
dataFile = new FileEditor( fileName ); }
TransactionProcessor.java Line 309
Create a FileEditor object from the file name

107. TransactionProcessor.java Line 323 Lines 336-337
311
catch( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error Opening File",
"IO Error", JOptionPane.ERROR_MESSAGE );
return false; }
317
return true;
319
} // end method openFile
321
// create, update or delete the record
private void performAction( String action ) {
try {
326
// get the textfield values
String[] values = userInterface.getFieldValues();
329
int accountNumber = Integer.parseInt( values[ BankUI.ACCOUNT ] );
String firstName = values[ BankUI.FIRSTNAME ];
String lastName = values[ BankUI.LASTNAME ];
double balance = Double.parseDouble( values[ BankUI.BALANCE ] );
334
if ( action.equals( "Create" ) )
dataFile.newRecord( accountNumber, // create a new record
firstName, lastName, balance );
TransactionProcessor.java Line 323 Lines
Called when the first action button is pressed
Create a new record

108. TransactionProcessor.java Lines 340-341 Line 344
338
else if ( action.equals( "Update" ) )
dataFile.updateRecord( accountNumber, // update record
firstName, lastName, balance );
342
else if ( action.equals( "Delete" ) )
dataFile.deleteRecord( accountNumber ); // delete record
345
else
JOptionPane.showMessageDialog( this, "Invalid Action",
"Error executing action", JOptionPane.ERROR_MESSAGE );
349
} // end try
351
catch( NumberFormatException format ) {
JOptionPane.showMessageDialog( this, "Bad Input",
"Number Format Error", JOptionPane.ERROR_MESSAGE ); }
356
catch( IllegalArgumentException badAccount ) {
JOptionPane.showMessageDialog( this, badAccount.getMessage(),
"Bad Account Number", JOptionPane.ERROR_MESSAGE ); }
catch( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error writing to the file",
"IO Error", JOptionPane.ERROR_MESSAGE ); }
Update a record
TransactionProcessor.java Lines Line 344
Delete a record

109. TransactionProcessor.java Line 369
365
} // end method performAction
367
// input a record in the textfields and update the balance
private void displayRecord( String transaction ) {
try {
// get the account number
int accountNumber = Integer.parseInt(
userInterface.getFieldValues()[ BankUI.ACCOUNT ] );
375
// get the associated record
RandomAccessAccountRecord record =
dataFile.getRecord( accountNumber );
379
if ( record.getAccount() == 0 )
JOptionPane.showMessageDialog( this, "Record does not exist",
"Bad Account Number", JOptionPane.ERROR_MESSAGE );
383
// get the transaction
double change = Double.parseDouble( transaction );
386
// create a string array to send to the textfields
String[] values = { String.valueOf( record.getAccount() ),
record.getFirstName(), record.getLastName(),
String.valueOf( record.getBalance() + change ),
"Charge(+) or payment (-)" };
TransactionProcessor.java Line 369
Display a record in the textfields

110. TransactionProcessor.java 392
userInterface.setFieldValues( values );
394
} // end try
396
catch( NumberFormatException format ) {
JOptionPane.showMessageDialog( this, "Bad Input",
"Number Format Error", JOptionPane.ERROR_MESSAGE ); }
401
catch ( IllegalArgumentException badAccount ) {
JOptionPane.showMessageDialog( this, badAccount.getMessage(),
"Bad Account Number", JOptionPane.ERROR_MESSAGE ); }
406
catch( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error reading the file",
"IO Error", JOptionPane.ERROR_MESSAGE ); }
411
} // end method displayRecord
413
414 } // end class TransactionProcessor
TransactionProcessor.java

111. FileEditor.java Line 15 Line 22
// Fig : FileEditor.java
// This class declares methods that manipulate bank account
// records in a random access file.
import java.io.*; 5
import com.deitel.jhtp5.ch17.RandomAccessAccountRecord; 7
public class FileEditor { 9
RandomAccessFile file; // reference to the file 11
// open the file
public FileEditor( File fileName ) throws IOException {
file = new RandomAccessFile( fileName, "rw" ); } 17
// close the file
public void closeFile() throws IOException {
if ( file != null )
file.close(); } 24
FileEditor.java Line 15 Line 22
Create a RandomAccessFile from the file name provided
Close the object’s file

112. FileEditor.java Line 26 Line 35 Line 37 Lines 44-45
// get a record from the file
public RandomAccessAccountRecord getRecord( int accountNumber )
throws IllegalArgumentException, NumberFormatException, IOException {
RandomAccessAccountRecord record = new RandomAccessAccountRecord(); 30
if ( accountNumber < 1 || accountNumber > 100 )
throw new IllegalArgumentException( "Out of range" ); 33
// seek appropriate record in file
file.seek( ( accountNumber - 1 ) * RandomAccessAccountRecord.SIZE ); 36
record.read( file ); 38
return record; 40
} // end method getRecord 42
// update record in file
public void updateRecord( int accountNumber, String firstName,
String lastName, double balance )
throws IllegalArgumentException, IOException {
RandomAccessAccountRecord record = getRecord( accountNumber );
if ( accountNumber == 0 )
throw new IllegalArgumentException( "Account does not exist" ); 51
Get a record from the file
FileEditor.java Line 26 Line 35 Line 37 Lines 44-45
Position the file pointer
Read a record
Update a record

113. FileEditor.java Line 53 Line 58 Lines 63-64 Line 73
// seek appropriate record in file
file.seek( ( accountNumber - 1 ) * RandomAccessAccountRecord.SIZE ); 54
record = new RandomAccessAccountRecord( accountNumber,
firstName, lastName, balance ); 57
record.write( file ); // write updated record to file 59
} // end method updateRecord 61
// add record to file
public void newRecord( int accountNumber, String firstName,
String lastName, double balance )
throws IllegalArgumentException, IOException {
RandomAccessAccountRecord record = getRecord( accountNumber ); 68
if ( record.getAccount() != 0 )
throw new IllegalArgumentException( "Account already exists" ); 71
// seek appropriate record in file
file.seek( ( accountNumber - 1 ) * RandomAccessAccountRecord.SIZE ); 74
record = new RandomAccessAccountRecord( accountNumber,
firstName, lastName, balance );
Position the file pointer
FileEditor.java Line 53 Line 58 Lines Line 73
Overwrite the record
Create a new record
Position the file pointer

114. FileEditor.java Line 78 Line 83 Line 92 Line 9677
record.write( file ); // write record to file 79
} // end method newRecord 81
// delete record from file
public void deleteRecord( int accountNumber )
throws IllegalArgumentException, IOException {
RandomAccessAccountRecord record = getRecord( accountNumber ); 87
if ( record.getAccount() == 0 )
throw new IllegalArgumentException( "Account does not exist" ); 90
// seek appropriate record in file
file.seek( ( accountNumber - 1 ) * RandomAccessAccountRecord.SIZE ); 93
// create a blank record to write to the file
record = new RandomAccessAccountRecord();
record.write( file ); 97
} // end method deleteRecord 99
100 } // end class EditFile
Write the new record
FileEditor.java Line 78 Line 83 Line 92 Line 96
Delete a record
Position the file pointer
Delete a record by overwriting the old record with a blank record

115. 17.13 New I/O APIs for the Java Platform
Buffers
Consolidate I/O operations
Four properties
Capacity
Limit
Position
Mark
Put and get operations
Relative or absolute
Clear, flip, rewind, reset

116. 17.13 New I/O APIs for the Java Platform
Channels
Connection to an I/O device
Interacts efficiently with buffers
ReadableByteChannel interface
Method read
WriteableByteChannel interface
Method write
Scattering reads and gather writes
Class FileChannel

117. 17.13 New I/O APIs for the Java Platform
File Locks
Restricts access to a portion of a file
FileChannel, position, size
Exclusive or shared
Charsets
Package java.nio.charset
Class Charset
Methods decode, encode
Class CharsetDecoder, CharsetEncoder

118. FileChannelTest.java Lines 4-5 Line 16
// Fig. 17.23: FileChannelTest.java
// Demonstrates FileChannel and ByteBuffer.
import java.io.*;
import java.nio.*;
import java.nio.channels.*; 6
public class FileChannelTest {
private FileChannel fileChannel; 9
// no-arg constructor
public FileChannelTest() {
// create random access file and get file channel
try {
RandomAccessFile file = new RandomAccessFile( "Test", "rw" );
fileChannel = file.getChannel(); }
catch ( IOException ioException ) {
ioException.printStackTrace(); } 21
} // end constructor FileChannelTest 23
FileChannelTest.java Lines 4-5 Line 16
Import the java.nio and java.nio.channels packages
Get a channel by calling method getChannel

119. FileChannelTest.java Line 28 Lines 31-33 Line 36 Line 37 Line 46
// write to writeChannel
public void writeToFile() throws IOException {
// create buffer for writing
ByteBuffer buffer = ByteBuffer.allocate( 14 ); 29
// write an int, a char and a double to buffer
buffer.putInt( 100 );
buffer.putChar( 'A' );
buffer.putDouble( ); 34
// flip buffer and write buffer to fileChannel
buffer.flip();
fileChannel.write( buffer ); } 39
// read from readChannel
public void readFromFile() throws IOException {
String content = ""; 44
// create buffer for read
ByteBuffer buffer = ByteBuffer.allocate( 14 ); 47
Allocate a buffer of 14 bytes
FileChannelTest.java Line 28 Lines Line 36 Line 37 Line 46
Fill the buffer with an integer, a character and a double
Flip the buffer to prepare it for writing
Write the buffer to the FileChannel
Allocate a buffer of 14 bytes

120. FileChannelTest.java Lines 49-50 Line 53 Lines 56-57 Line 62
// read buffer from fileChannel
fileChannel.position( 0 );
fileChannel.read( buffer ); 51
// flip buffer for reading
buffer.flip(); 54
// obtain content
content += buffer.getInt() + ", " + buffer.getChar() + ", " +
buffer.getDouble(); 58
System.out.println( "File contains: " + content ); 60
// close fileChannel
fileChannel.close(); 63
} // end method readFromFile 65
public static void main( String[] args ) {
FileChannelTest application = new FileChannelTest(); 69
Position the FileChannel at the beginning and fill the buffer with bytes
FileChannelTest.java Lines Line 53 Lines Line 62
Flip the buffer to prepare it for reading
Fill the buffer with an integer, a character and a double
Close the FileChannel

121. FileChannelTest.java 70 // write to file and then read from file
try {
application.writeToFile();
application.readFromFile(); }
catch ( IOException ioException ) {
ioException.printStackTrace(); } } 79
80 } // end class FileChannelTest
FileChannelTest.java
File contains: 100, A, 12.34