CSC 245 Chapter 7, Spring 2013

 1992-2007 Pearson Education, Inc. All rights reserved. Azzam Mourad 1 77 Files and Streams Azzam Mourad 2 OBJECTIVES In this chapter you will learn:  To create, read, write and update files.  To use class File to retrieve information about files and directories.  The Java input/output stream class hierarchy.  The differences between text files and binary files.  Sequential-access and random-access file processing.  To use classes Scanner and Formatter to process text files.  To use the FileInputStream and FileOutputStream classes.  To use a JFileChooser dialog.  To use the ObjectInputStream and ObjectOutputStream classes Azzam Mourad 3 14.1    Introduction 14.2    Data Hierarchy 14.3    Files and Streams 14.4    Class File 14.5    Sequential-Access Text Files 14.5.1 Creating a Sequential-Access Text File 14.5.2   Reading Data from a Sequential-Access Text File 14.5.3 Case Study: A Credit-Inquiry Program 14.5.4 Updating Sequential-Access Files Azzam Mourad 4 14.6    Object Serialization 14.6.1 Creating a Sequential-Access File Using Object Serialization 14.6.2 Reading and Deserializing Data from a Sequential- Access File 14.7    Additional java.io Classes 14.8    Opening Files with JFileChooser 14.9   Wrap-Up Azzam Mourad 5 14.1 Introduction • Storage of data in variables and arrays is temporary • Files used for long-term retention of large amounts of data, even after the programs that created the data terminate • Persistent data – exists beyond the duration of program execution • Files stored on secondary storage devices • Stream – ordered data that is read from or written to a file Azzam Mourad 6 14.3 Files and Streams • Java views each files as a sequential stream of bytes • Operating system provides mechanism to determine end of file – End-of-file marker – Count of total bytes in file – Java program processing a stream of bytes receives an indication from the operating system when program reaches end of stream Azzam Mourad 7 14.3 Files and Streams • File streams – Byte-based streams – stores data in binary format • Binary files – created from byte-based streams, read by a program that converts data to human-readable format – Character-based streams – stores data as a sequence of characters • Text files – created from character-based streams, can be read by text editors • Java opens file by creating an object and associating a stream with it • Standard streams – each stream can be redirected – System.in – standard input stream object, can be redirected with method setIn – System.out – standard output stream object, can be redirected with method setOut – System.err – standard error stream object, can be redirected with method setErr Azzam Mourad 8 14.3 Files and Streams •java.io classes – FileInputStream and FileOutputStream – byte- based I/O – FileReader and FileWriter – character-based I/O – ObjectInputStream and ObjectOutputStream – used for input and output of objects or variables of primitive data types – File – useful for obtaining information about files and directories • Classes Scanner and Formatter – Scanner – can be used to easily read data from a file – Formatter – can be used to easily write data to a file Azzam Mourad 9 14.4 Class File • Class File useful for retrieving information about files and directories from disk • Objects of class File do not open files or provide any file-processing capabilities Azzam Mourad 10 Creating File Objects • Class File provides four constructors: 1. Takes String specifying name and path (location of file on disk) 2. Takes two Strings, first specifying path and second specifying name of file 3. Takes File object specifying path and String specifying name of file 4. Takes URI object specifying name and location of file • Different kinds of paths – Absolute path – contains all directories, starting with the root directory, that lead to a specific file or directory – Relative path – normally starts from the directory in which the application began executing Azzam Mourad 11 Error-Prevention Tip 14.1 Use File method isFile to determine whether a File object represents a file (not a directory) before attempting to open the file. Azzam Mourad 12 Demonstrating Class File • Common File methods – exists – return true if file exists where it is specified – isFile – returns true if File is a file, not a directory – isDirectory – returns true if File is a directory – getPath – return file path as a string – list – retrieve contents of a directory • Separator character – used to separate directories and files in a path – Windows uses \ – UNIX uses / – Java process both characters, File.pathSeparator can be used to obtain the local computer’s proper separator character Azzam Mourad 13 1 // Fig. 14.4: FileDemonstration.java 2 // Demonstrating the File class. 3 import java.io.File; 4 5 public class FileDemonstration 6 { 7 // display information about file user specifies 8 public void analyzePath( String path ) 9 { 10 // create File object based on user input 11 File name = new File( path ); 12 13 if ( name.exists() ) // if name exists, output information about it 14 { 15 // display file (or directory) information 16 System.out.printf( 17 "%s%s\n%s\n%s\n%s\n%s%s\n%s%s\n%s%s\n%s%s\n%s%s", 18 name.getName(), " exists", 19 ( name.isFile() ? "is a file" : "is not a file" ), 20 ( name.isDirectory() ? "is a directory" : 21 "is not a directory" ), 22 ( name.isAbsolute() ? "is absolute path" : 23 "is not absolute path" ), "Last modified: ", 24 name.lastModified(), "Length: ", name.length(), 25 "Path: ", name.getPath(), "Absolute path: ", 26 name.getAbsolutePath(), "Parent: ", name.getParent() ); 27 Create new File object; user specifies file name and path Returns true if file or directory specified exists Retrieve name of file or directory Returns true if name is a file, not a directory Returns true if name is a directory, not a file Returns true if path was an absolute path Retrieve time file or directory was last modified (system- dependent value) Retrieve length of file in bytes Retrieve path entered as a string Retrieve absolute path of file or directoryRetrieve parent directory (path where File object’s file or directory can be found) Azzam Mourad 14 28 if ( name.isDirectory() ) // output directory listing 29 { 30 String directory[] = name.list(); 31 System.out.println( "\n\nDirectory contents:\n" ); 32 33 for ( String directoryName : directory ) 34 System.out.printf( "%s\n", directoryName ); 35 } // end else 36 } // end outer if 37 else // not file or directory, output error message 38 { 39 System.out.printf( "%s %s", path, "does not exist." ); 40 } // end else 41 } // end method analyzePath 42 } // end class FileDemonstration Returns true if File is a directory, not a file Retrieve and display contents of directory Azzam Mourad 15 1 // Fig. 14.5: FileDemonstrationTest.java 2 // Testing the FileDemonstration class. 3 import java.util.Scanner; 4 5 public class FileDemonstrationTest 6 { 7 public static void main( String args[] ) 8 { 9 Scanner input = new Scanner( System.in ); 10 FileDemonstration application = new FileDemonstration(); 11 12 System.out.print( "Enter file or directory name here: " ); 13 application.analyzePath( input.nextLine() ); 14 } // end main 15 } // end class FileDemonstrationTest Azzam Mourad 16 Enter file or directory name here: C:\Program Files\Java\jdk1.5.0\demo\jfc jfc exists is not a file is a directory is absolute path Last modified: 1083938776645 Length: 0 Path: C:\Program Files\Java\jdk1.5.0\demo\jfc Absolute path: C:\Program Files\Java\jdk1.5.0\demo\jfc Parent: C:\Program Files\Java\jdk1.5.0\demo Directory contents: CodePointIM FileChooserDemo Font2DTest Java2D Metalworks Notepad SampleTree Stylepad SwingApplet SwingSet2 TableExample Azzam Mourad 17 Outline FileDemonstration Test.java (3 of 3) Enter file or directory name here: C:\Program Files\Java\jdk1.5.0\demo\jfc\Java2D\readme.txt readme.txt exists is a file is not a directory is absolute path Last modified: 1083938778347 Length: 7501 Path: C:\Program Files\Java\jdk1.5.0\demo\jfc\Java2D\readme.txt Absolute path: C:\Program Files\Java\jdk1.5.0\demo\jfc\Java2D\readme.txt Parent: C:\Program Files\Java\jdk1.5.0\demo\jfc\Java2D Azzam Mourad 18 Common Programming Error 14.1 Using \ as a directory separator rather than \\ in a string literal is a logic error. A single \ indicates that the \ followed by the next character represents an escape sequence. Use \\ to insert a \ in a string literal. Azzam Mourad 19 14.5 Sequential-Access Text Files • Records are stored in order by record-key field • Can be created as text files or binary files Azzam Mourad 20 14.5.1 Creating a Sequential-Access Text File • Java imposes no structure on a file, records do not exist as part of the Java language • Programmer must structure files •Formatter class can be used to open a text file for writing – Pass name of file to constructor – If file does not exist, will be created – If file already exists, contents are truncated (discarded) – Use method format to write formatted text to file – Use method close to close the Formatter object (if method not called, OS normally closes file when program exits) Azzam Mourad 21 14.5.1 Creating a Sequential-Access Text File • Possible exceptions – SecurityException – occurs when opening file using Formatter object, if user does not have permission to write data to file – FileNotFoundException – occurs when opening file using Formatter object, if file cannot be found and new file cannot be created – NoSuchElementException – occurs when invalid input is read in by a Scanner object – FormatterClosedException – occurs when an attempt is made to write to a file using an already closed Formatter object Azzam Mourad 22 1 // Fig. 14.6: AccountRecord.java 2 // A class that represents one record of information. 3 package com.deitel.jhtp7.ch14; // packaged for reuse 4 5 public class AccountRecord 6 { 7 private int account; 8 private String firstName; 9 private String lastName; 10 private double balance; 11 12 // no-argument constructor calls other constructor with default values 13 public AccountRecord() 14 { 15 this( 0, "", "", 0.0 ); // call four-argument constructor 16 } // end no-argument AccountRecord constructor 17 18 // initialize a record 19 public AccountRecord( int acct, String first, String last, double bal ) 20 { 21 setAccount( acct ); 22 setFirstName( first ); 23 setLastName( last ); 24 setBalance( bal ); 25 } // end four-argument AccountRecord constructor 26 Azzam Mourad 23 27 // set account number 28 public void setAccount( int acct ) 29 { 30 account = acct; 31 } // end method setAccount 32 33 // get account number 34 public int getAccount() 35 { 36 return account; 37 } // end method getAccount 38 39 // set first name 40 public void setFirstName( String first ) 41 { 42 firstName = first; 43 } // end method setFirstName 44 45 // get first name 46 public String getFirstName() 47 { 48 return firstName; 49 } // end method getFirstName 50 51 // set last name 52 public void setLastName( String last ) 53 { 54 lastName = last; 55 } // end method setLastName 56 Azzam Mourad 24 57 // get last name 58 public String getLastName() 59 { 60 return lastName; 61 } // end method getLastName 62 63 // set balance 64 public void setBalance( double bal ) 65 { 66 balance = bal; 67 } // end method setBalance 68 69 // get balance 70 public double getBalance() 71 { 72 return balance; 73 } // end method getBalance 74 } // end class AccountRecord Azzam Mourad 25 1 // Fig. 14.7: CreateTextFile.java 2 // Writing data to a text file with class Formatter. 3 import java.io.FileNotFoundException; 4 import java.lang.SecurityException; 5 import java.util.Formatter; 6 import java.util.FormatterClosedException; 7 import java.util.NoSuchElementException; 8 import java.util.Scanner; 9 10 import com.deitel.jhtp7.ch14.AccountRecord; 11 12 public class CreateTextFile 13 { 14 private Formatter output; // object used to output text to file 15 16 // enable user to open file 17 public void openFile() 18 { 19 try 20 { 21 output = new Formatter( "clients.txt" ); 22 } // end try 23 catch ( SecurityException securityException ) 24 { 25 System.err.println( 26 "You do not have write access to this file." ); 27 System.exit( 1 ); 28 } // end catch Used for retrieving input from user Used for writing data to file Object used to output data to file Open file clients.txt for writing Azzam Mourad 26 29 catch ( FileNotFoundException filesNotFoundException ) 30 { 31 System.err.println( "Error creating file." ); 32 System.exit( 1 ); 33 } // end catch 34 } // end method openFile 35 36 // add records to file 37 public void addRecords() 38 { 39 // object to be written to file 40 AccountRecord record = new AccountRecord(); 41 42 Scanner input = new Scanner( System.in ); 43 44 System.out.printf( "%s\n%s\n%s\n%s\n\n", 45 "To terminate input, type the end-of-file indicator ", 46 "when you are prompted to enter input.", 47 "On UNIX/Linux/Mac OS X type <ctrl> d then press Enter", 48 "On Windows type <ctrl> z then press Enter" ); 49 50 System.out.printf( "%s\n%s", 51 "Enter account number (> 0), first name, last name and balance.", 52 "? " ); 53 Create Scanner to retrieve input from user Create AccountRecord to be filled with user input Azzam Mourad 27 54 while ( input.hasNext() ) // loop until end-of-file indicator 55 { 56 try // output values to file 57 { 58 // retrieve data to be output 59 record.setAccount( input.nextInt() ); // read account number 60 record.setFirstName( input.next() ); // read first name 61 record.setLastName( input.next() ); // read last name 62 record.setBalance( input.nextDouble() ); // read balance 63 64 if ( record.getAccount() > 0 ) 65 { 66 // write new record 67 output.format( "%d %s %s %.2f\n", record.getAccount(), 68 record.getFirstName(), record.getLastName(), 69 record.getBalance() ); 70 } // end if 71 else 72 { 73 System.out.println( 74 "Account number must be greater than 0." ); 75 } // end else 76 } // end try 77 catch ( FormatterClosedException formatterClosedException ) 78 { 79 System.err.println( "Error writing to file." ); 80 return; 81 } // end catch Loop while user is entering input Retrieve input, store data in AccountRecord Write AccountRecord information to file File closed while trying to write to it Azzam Mourad 28 82 catch ( NoSuchElementException elementException ) 83 { 84 System.err.println( "Invalid input. Please try again." ); 85 input.nextLine(); // discard input so user can try again 86 } // end catch 87 88 System.out.printf( "%s %s\n%s", "Enter account number (>0),", 89 "first name, last name and balance.", "? " ); 90 } // end while 91 } // end method addRecords 92 93 // close file 94 public void closeFile() 95 { 96 if ( output != null ) 97 output.close(); 98 } // end method closeFile 99 } // end class CreateTextFile Close file Error with input entered by user Azzam Mourad 29 1 // Fig. 14.9: CreateTextFileTest.java 2 // Testing the CreateTextFile class. 3 4 public class CreateTextFileTest 5 { 6 public static void main( String args[] ) 7 { 8 CreateTextFile application = new CreateTextFile(); 9 10 application.openFile(); 11 application.addRecords(); 12 application.closeFile(); 13 } // end main 14 } // end class CreateTextFileTest Azzam Mourad 30 To terminate input, type the end-of-file indicator when you are prompted to enter input. On UNIX/Linux/Mac OS X type <ctrl> d then press Enter On Windows type <ctrl> z then press Enter Enter account number (> 0), first name, last name and balance. ? 100 Bob Jones 24.98 Enter account number (> 0), first name, last name and balance. ? 200 Steve Doe -345.67 Enter account number (> 0), first name, last name and balance. ? 300 Pam White 0.00 Enter account number (> 0), first name, last name and balance. ? 400 Sam Stone -42.16 Enter account number (> 0), first name, last name and balance. ? 500 Sue Rich 224.62 Enter account number (> 0), first name, last name and balance. ? ^Z Azzam Mourad 31 Fig.14.10 | Sample data for the program in Fig. 14.7. Sample data 100 Bob Jones 24.98 200 Steve Doe -345.67 300 Pam White 0.00 400 Sam Stone -42.16 500 Sue Rich 224.62 Azzam Mourad 32 14.5.2 Reading Data from a Sequential- Access Text File • Data is stored in files so that it may be retrieved for processing when needed •Scanner object can be used to read data sequentially from a text file – Pass File object representing file to be read to Scanner constructor – FileNotFoundException occurs if file cannot be found – Data read from file using same methods as for keyboard input – nextInt, nextDouble, next, etc. – IllegalStateException occurs if attempt is made to read from closed Scanner object Azzam Mourad 33 1 // Fig. 14.11: ReadTextFile.java 2 // This program reads a text file and displays each record. 3 import java.io.File; 4 import java.io.FileNotFoundException; 5 import java.lang.IllegalStateException; 6 import java.util.NoSuchElementException; 7 import java.util.Scanner; 8 9 import com.deitel.jhtp7.ch14.AccountRecord; 10 11 public class ReadTextFile 12 { 13 private Scanner input; 14 15 // enable user to open file 16 public void openFile() 17 { 18 try 19 { 20 input = new Scanner( new File( "clients.txt" ) ); 21 } // end try 22 catch ( FileNotFoundException fileNotFoundException ) 23 { 24 System.err.println( "Error opening file." ); 25 System.exit( 1 ); 26 } // end catch 27 } // end method openFile 28 Open file clients.txt for reading Azzam Mourad 34 29 // read record from file 30 public void readRecords() 31 { 32 // object to be written to screen 33 AccountRecord record = new AccountRecord(); 34 35 System.out.printf( "%-10s%-12s%-12s%10s\n", "Account", 36 "First Name", "Last Name", "Balance" ); 37 38 try // read records from file using Scanner object 39 { 40 while ( input.hasNext() ) 41 { 42 record.setAccount( input.nextInt() ); // read account number 43 record.setFirstName( input.next() ); // read first name 44 record.setLastName( input.next() ); // read last name 45 record.setBalance( input.nextDouble() ); // read balance 46 47 // display record contents 48 System.out.printf( "%-10d%-12s%-12s%10.2f\n", 49 record.getAccount(), record.getFirstName(), 50 record.getLastName(), record.getBalance() ); 51 } // end while 52 } // end try Create AccountRecord to store input from file While there is data to be read from file Display AccountRecord contents Read data from file, store in AccountRecord Azzam Mourad 35 53 catch ( NoSuchElementException elementException ) 54 { 55 System.err.println( "File improperly formed." ); 56 input.close(); 57 System.exit( 1 ); 58 } // end catch 59 catch ( IllegalStateException stateException ) 60 { 61 System.err.println( "Error reading from file." ); 62 System.exit( 1 ); 63 } // end catch 64 } // end method readRecords 65 66 // close file and terminate application 67 public void closeFile() 68 { 69 if ( input != null ) 70 input.close(); // close file 71 } // end method closeFile 72 } // end class ReadTextFile Close file Azzam Mourad 36 1 // Fig. 14.12: ReadTextFileTest.java 2 // This program test class ReadTextFile. 3 4 public class ReadTextFileTest 5 { 6 public static void main( String args[] ) 7 { 8 ReadTextFile application = new ReadTextFile(); 9 10 application.openFile(); 11 application.readRecords(); 12 application.closeFile(); 13 } // end main 14 } // end class ReadTextFileTest Account First Name Last Name Balance 100 Bob Jones 24.98 200 Steve Doe -345.67 300 Pam White 0.00 400 Sam Stone -42.16 500 Sue Rich 224.62 Azzam Mourad 37 14.5.3 Case Study: A Credit-Inquiry Program • To retrieve data sequentially from a file, programs normally start reading from beginning of the file and read all the data consecutively until desired information is found • Class Scanner provides no way to reposition to beginning of file • Instead, file is closed and reopened Azzam Mourad 38 14.5.4 Updating Sequential-Access Files • Data in many sequential files cannot be modified without risk of destroying other data in file • Old data cannot be overwritten if new data is not same size • Records in sequential-access files are not usually updated in place. Instead, entire file is usually rewritten. Azzam Mourad 39 Creating a Sequential-Access Binary File Constructor Summary • FileOutputStream(File file) Creates a file output stream to write to the file represented by the specified File object. • FileOutputStream(File file, boolean append) Creates a file output stream to write to the file represented by the specified File object. • FileOutputStream(String name) Creates an output file stream to write to the file with the specified name. • FileOutputStream(String name, boolean append) Creates an output file stream to write to the file with the specified name. Azzam Mourad 40 Creating a Sequential-Access Binary File Method Summary Void close() Closes this file output stream and releases any system resources associated with this stream.protected Void finalize() Cleans up the connection to the file, and ensures that the close method of this file output stream is called when there are no more references to this stream. Void write(byte[] b) Writes b.length bytes from the specified byte array to this file output stream. Void write(byte[] b, int off, int len) Writes len bytes from the specified byte array starting at offset off to this file output stream. voidwrite(int b) Writes the specified byte to this file output stream. Azzam Mourad 41 Reading a Sequential-Access Binary File Constructor Summary FileInputStream(File file) Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system. FileInputStream(String name) Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system. Azzam Mourad 42 Reading a Sequential-Access Binary File Method Summary Int available() Returns the number of bytes that can be read from this file input stream without blocking. Void close() Closes this file input stream and releases any system resources associated with the stream.protected Int read() Reads a byte of data from this input stream. Int read(byte[] b) Reads up to b.length bytes of data from this input stream into an array of bytes. Int read(byte[] b, int off, int len) Reads up to len bytes of data from this input stream into an array of bytes. Long skip(long n) Skips over and discards n bytes of data from the input stream. Azzam Mourad 43 14.6 Object Serialization • With text files, data type information lost • Object serialization – mechanism to read or write an entire object from a file • Serialized object – object represented as sequence of bytes, includes object’s data and type information about object • Deserialization – recreate object in memory from data in file • Serialization and deserialization performed with classes ObjectInputStream and ObjectOutputStream, methods readObject and writeObject Azzam Mourad 44 14.6.1 Creating a Sequential-Access File Using Object Serialization: Defining the AccountRecordSerializable Class •Serializable interface – programmers must declare a class to implement the Serializable interface, or objects of that class cannot be written to a file • To open a file for writing objects, create a FileOutputStream wrapped by an ObjectOutputStream – FileOutputStream provides methods for writing byte- based output to a file – ObjectOutputStream uses FileOutputStream to write objects to file – ObjectOutputStream method writeObject writes object to output file – ObjectOutputStream method close closes both objects Azzam Mourad 45 1 // Fig. 14.17: AccountRecordSerializable.java 2 // A class that represents one record of information. 3 package com.deitel.jhtp7.ch14; // packaged for reuse 4 5 import java.io.Serializable; 6 7 public class AccountRecordSerializable implements Serializable 8 { 9 private int account; 10 private String firstName; 11 private String lastName; 12 private double balance; 13 14 // no-argument constructor calls other constructor with default values 15 public AccountRecordSerializable() 16 { 17 this( 0, "", "", 0.0 ); 18 } // end no-argument AccountRecordSerializable constructor 19 20 // four-argument constructor initializes a record 21 public AccountRecordSerializable( 22 int acct, String first, String last, double bal ) 23 { 24 setAccount( acct ); 25 setFirstName( first ); 26 setLastName( last ); 27 setBalance( bal ); 28 } // end four-argument AccountRecordSerializable constructor 29 Interface Serializable specifies that AccountRecordSerializable objects can be written to file Azzam Mourad 46 30 // set account number 31 public void setAccount( int acct ) 32 { 33 account = acct; 34 } // end method setAccount 35 36 // get account number 37 public int getAccount() 38 { 39 return account; 40 } // end method getAccount 41 42 // set first name 43 public void setFirstName( String first ) 44 { 45 firstName = first; 46 } // end method setFirstName 47 48 // get first name 49 public String getFirstName() 50 { 51 return firstName; 52 } // end method getFirstName 53 54 // set last name 55 public void setLastName( String last ) 56 { 57 lastName = last; 58 } // end method setLastName 59 Azzam Mourad 47 60 // get last name 61 public String getLastName() 62 { 63 return lastName; 64 } // end method getLastName 65 66 // set balance 67 public void setBalance( double bal ) 68 { 69 balance = bal; 70 } // end method setBalance 71 72 // get balance 73 public double getBalance() 74 { 75 return balance; 76 } // end method getBalance 77 } // end class AccountRecordSerializable Azzam Mourad 48 1 // Fig. 14.18: CreateSequentialFile.java 2 // Writing objects sequentially to a file with class ObjectOutputStream. 3 import java.io.FileOutputStream; 4 import java.io.IOException; 5 import java.io.ObjectOutputStream; 6 import java.util.NoSuchElementException; 7 import java.util.Scanner; 8 9 import com.deitel.jhtp7.ch14.AccountRecordSerializable; 10 11 public class CreateSequentialFile 12 { 13 private ObjectOutputStream output; // outputs data to file 14 15 // allow user to specify file name 16 public void openFile() 17 { 18 try // open file 19 { 20 output = new ObjectOutputStream( 21 new FileOutputStream( "clients.ser" ) ); 22 } // end try 23 catch ( IOException ioException ) 24 { 25 System.err.println( "Error opening file." ); 26 } // end catch 27 } // end method openFile 28 Class used to create byte-based output stream Class used to create output object data to byte- based stream Open file clients.ser for writing Azzam Mourad 49 29 // add records to file 30 public void addRecords() 31 { 32 AccountRecordSerializable record; // object to be written to file 33 int accountNumber = 0; // account number for record object 34 String firstName; // first name for record object 35 String lastName; // last name for record object 36 double balance; // balance for record object 37 38 Scanner input = new Scanner( System.in ); 39 40 System.out.printf( "%s\n%s\n%s\n%s\n\n", 41 "To terminate input, type the end-of-file indicator ", 42 "when you are prompted to enter input.", 43 "On UNIX/Linux/Mac OS X type <ctrl> d then press Enter", 44 "On Windows type <ctrl> z then press Enter" ); 45 46 System.out.printf( "%s\n%s", 47 "Enter account number (> 0), first name, last name and balance.", 48 "? " ); 49 50 while ( input.hasNext() ) // loop until end-of-file indicator 51 { 52 try // output values to file 53 { 54 accountNumber = input.nextInt(); // read account number 55 firstName = input.next(); // read first name 56 lastName = input.next(); // read last name 57 balance = input.nextDouble(); // read balance 58 Azzam Mourad 50 59 if ( accountNumber > 0 ) 60 { 61 // create new record 62 record = new AccountRecordSerializable( accountNumber, 63 firstName, lastName, balance ); 64 output.writeObject( record ); // output record 65 } // end if 66 else 67 { 68 System.out.println( 69 "Account number must be greater than 0." ); 70 } // end else 71 } // end try 72 catch ( IOException ioException ) 73 { 74 System.err.println( "Error writing to file." ); 75 return; 76 } // end catch 77 catch ( NoSuchElementException elementException ) 78 { 79 System.err.println( "Invalid input. Please try again." ); 80 input.nextLine(); // discard input so user can try again 81 } // end catch 82 83 System.out.printf( "%s %s\n%s", "Enter account number (>0),", 84 "first name, last name and balance.", "? " ); 85 } // end while 86 } // end method addRecords 87 Create AccountRecord based on user input Write record object to file Azzam Mourad 51 88 // close file and terminate application 89 public void closeFile() 90 { 91 try // close file 92 { 93 if ( output != null ) 94 output.close(); 95 } // end try 96 catch ( IOException ioException ) 97 { 98 System.err.println( "Error closing file." ); 99 System.exit( 1 ); 100 } // end catch 101 } // end method closeFile 102 } // end class CreateSequentialFile Azzam Mourad 52 1 // Fig. 14.19: CreateSequentialFileTest.java 2 // Testing class CreateSequentialFile. 3 4 public class CreateSequentialFileTest 5 { 6 public static void main( String args[] ) 7 { 8 CreateSequentialFile application = new CreateSequentialFile(); 9 10 application.openFile(); 11 application.addRecords(); 12 application.closeFile(); 13 } // end main 14 } // end class CreateSequentialFileTest To terminate input, type the end-of-file indicator when you are prompted to enter input. On UNIX/Linux/Mac OS X type <ctrl> d then press Enter On Windows type <ctrl> z then press Enter Enter account number (> 0), first name, last name and balance. ? 100 Bob Jones 24.98 Enter account number (> 0), first name, last name and balance. ? 200 Steve Doe -345.67 Enter account number (> 0), first name, last name and balance. ? 300 Pam White 0.00 Enter account number (> 0), first name, last name and balance. ? 400 Sam Stone -42.16 Enter account number (> 0), first name, last name and balance. ? 500 Sue Rich 224.62 Enter account number (> 0), firs