Files CSC 171 FALL 2001 LECTURE 18

History Operating Systems Operating systems (originally called monitors or supervisors) had been developed in the late 1950s Users were frustrated by their lack of intimacy with the computer Fernando Corbató, MIT, produced CTSS (Compatible Time Sharing System) for the IBM 7090/94, the first effective time-sharing system and coincidentally the first practical means of remote access.

History By the mid-1960's the jet airliner (and Boeing) had revolutionized the airline travel business but the reservation process was inadequate. After remote access had been proven by the CTSS system, IBM produced the first large scale, on-line, real-time reservation tracking system, named SABRE for American Airlines, and soon to be copied by others.

History III 1962 – The first video game (Spacewar) is invented by MIT grad student Steve Russel

File IO We have seen character I/O Sometimes, we want to have other data types stored in file – It’s all just bits

Consider saving an array a = new float[5][5]; for(int i = 0 ; i<a.length;i++) for(int j = 0 ; j<a[i].length;j++) a[i][j] = ((float)i+1) / ((float)j+1) ;

Open the File private void saveArray() { try { JFileChooser chooser = new JFileChooser(); PrintWriter out1 = null; if (chooser.showOpenDialog(null)== JFileChooser.APPROVE_OPTION) { File selectedFile = chooser.getSelectedFile(); FileWriter writer = new FileWriter(selectedFile); out1 = new PrintWriter(writer);

Write the array for(int i = 0 ; i<a.length;i++) for(int j = 0 ; j<a[i].length;j++){ out1.println(a[i][j] + " "); System.out.println(" " + a[i][j]); } writer.close(); } } catch (IOException e) {System.out.println("problem");} }

Open the file private void restoreArray() { try { JFileChooser chooser = new JFileChooser(); BufferedReader in1 = null; if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) { File selectedFile = chooser.getSelectedFile(); FileReader reader = new FileReader(selectedFile); in1 = new BufferedReader(reader);

Read the array for(int i = 0 ; i<a.length;i++) for(int j = 0 ; j<a[i].length;j++){ String s1 = in1.readLine(); System.out.println(s1); a[i][j] = (float) Double.parseDouble(s1); } reader.close(); } } catch (IOException e) {System.out.println("problem");} repaint(); }

Text File

Byte by Byte Text file 303 bytes \r \n \r \n \r \n \r \n 0. 2 \r \n \r \n \r \n \r \n 0. 5 \r \n 0. 4 \r \n \r \n \r \n 1. 0 \r \n \r \n \r \n 4. 0 \r \n \r \n \r \n \r \n 0. 8 \r \n 5. 0 \r \n \r \n \r \n \r \n 1. 0 \r \n

Open the file (binary) private void saveArray2() { try { JFileChooser chooser = new JFileChooser(); DataOutputStream out1 = null; if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) { File selectedFile = chooser.getSelectedFile(); FileOutputStream writer = new FileOutputStream(selectedFile); out1 = new DataOutputStream(writer);

Write the file for(int i = 0 ; i<a.length;i++) for(int j = 0 ; j<a[i].length;j++){ out1.writeFloat(a[i][j]); System.out.println(" " + a[i][j]); } writer.close(); } } catch (IOException e) {System.out.println("problem");} }

Open the file private void restoreArray2() { try { JFileChooser chooser = new JFileChooser(); DataInputStream in1 = null; if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) { File selectedFile = chooser.getSelectedFile(); FileInputStream reader = new FileInputStream(selectedFile); in1 = new DataInputStream(reader);

Read the file for(int i = 0 ; i<a.length;i++) for(int j = 0 ; j<a[i].length;j++){ a[i][j] = in1.readFloat(); } reader.close(); } } catch (IOException e) {System.out.println("problem");} repaint(); }

Same data Bytes e e e e e e e e e e e e e e e e e e e e e e e e e+00

Data Streams close() readBoolean() readByte() readChar() readDouble() readFloat() readInt() readLong() readShort() readLine() flush() close() writeByte(int b) writeBoolean(boolean v) writeBytes(String s) writeChar(int v) writeChars(String s) writeDouble(Double v) writeFloat(Float v) writeInt(int v) writeLong(long v) writeShort(int v)

Serializable Objects We can write whole objects to files

public AccountRecord( int acct, String first, String last, double bal ) { setAccount( acct ); setFirstName( first ); setLastName( last ); setBalance( bal ); } public void setAccount( int acct ) { account = acct; } public int getAccount() { return account; } public void setFirstName( String first ) { firstName = first; } public String getFirstName() { return firstName; } public void setLastName( String last ) { lastName = last; } public String getLastName() { return lastName; } public void setBalance( double bal ) { balance = bal; } public double getBalance() { return balance; } public String toString(){ return "Account Record " + " " + account + " " + firstName + " " + lastName + " " + balance; }

// Java core packages import java.io.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class CreateSequentialFile extends JFrame{ private ObjectOutputStream output; public CreateSequentialFile(){ AccountRecord record; openFile(); try { // create new record record = new AccountRecord( 1, "Ted","Pawlicki",100); System.out.println(record.toString()); output.writeObject( record ); output.flush(); // create new record record = new AccountRecord( 2, "Adam","Frank",2000); System.out.println(record.toString()); output.writeObject( record ); output.flush();

// 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 ); int result = fileChooser.showSaveDialog(this); // get selected file File fileName = fileChooser.getSelectedFile(); // display error if invalid if ( fileName == null || fileName.getName().equals( "" ) ){ System.err.println( "Invalid File Name"); return; } else {// open file try { output = new ObjectOutputStream( new FileOutputStream( fileName ) ); } // process exceptions from opening file catch ( IOException ioException ) { System.err.println( "Error Opening File"); return; } } // end method openFile

// close file and terminate application private void closeFile() { // close file try { output.close(); System.exit( 0 ); } // process exceptions from closing file catch( IOException ioException ) { System.err.println( "Error closing file"); System.exit( 1 ); } public static void main( String args[] ) { new CreateSequentialFile(); }

public ReadSequentialFile(){ AccountRecord record; openFile(); try { // create new record record = (AccountRecord) input.readObject(); System.out.println(record.toString()); record = (AccountRecord) input.readObject(); System.out.println(record.toString()); record = (AccountRecord) input.readObject(); System.out.println(record.toString()); } catch(ClassNotFoundException e) { System.err.println(" Problem with class "); System.exit(1); } catch(IOException e) { System.err.println(" Problem with file "); System.exit(1); } closeFile(); }

\0 005 s r \0 \r A c c o u n t R e c o r d G \r 002 \ I \0 007 a c c o u n t D \0 007 b a l a n c e L \0 \t f i r s t N a m e t \0 022 L j a v a / l a n g / S t r i n g ; L \0 \b l a s t N a m e q \0 ~ \0 001 x p \0 \0 \0 Y \0 \0 \ \0 \0 \0 t \0 003 T e d t \0 \b P a w l i c k i s q \0 ~ \0 \0 \0 \0 \0 237 \0 \0 \0 \0 \0 t \0 004 A d a m t \ F r a n k s q \0 ~ \0 \0 \0 \0 \0 003 A c \0 \0 \0 \0 t \0 003 J o e t \ S c h m o