Streams CSC 171 FALL 2004 LECTURE 22. Make up exam Friday 12/3 11AM-12:10PM.

StreamsStreams

CSC 171 FALL 2004

LECTURE 22

Make up examMake up exam

Friday 12/3 11AM-12:10PM

READING ASSIGNMENTREADING ASSIGNMENT

Horstmann Chapter 15 – StreamsHorstmann Chapter 14 – Exceptions

Optional– Horstmann Chapter 16 – System Design– Horstmann Chapter 17, 18, 19

Prep for CSC 172

EXAMEXAM

In class 12/9– Arrays– Exceptions– Streams

StreamsStreams

In Java a stream provides access to sequences of bytes.

Bytes can come from a variety of sources– Console input/output– Files stored on the computer’s disk– Network connections

_________ access sequences of bytes.

___Streams______ access sequences of bytes.

Simplest File inputSimplest File input

Create a FileReader Use its read method to read a single

character-returns the next char as an int or the integer -1 at end of input

Test for -1 If not -1, cast to char Close the file when done

___________ and ________________ access sequences of characters.

_readers______ and ____writers____ access sequences of characters.

ReadingReadingFileReader reader = new FileReader("input.txt");

int next = reader.read() ;

char c;

if (next != -1)

c = (char)next();

...

reader.close()

WritingWriting

FileWriter writer = new FileWriter("output.txt");...char c='';...writer.write(c);

...write.close();

The read method returns an _________________,

either ___________ at end of file, or another value which needs to be cast to ___________, or ___________.

The read method returns an ___integer_____,

either ____-1_______ at end of file, or another value which needs to be cast to ___char____, or ____byte_______.

You must _______________ files that you no longer need.

You must ___close______ files that you no longer need.

TEXT FORMATTEXT FORMAT

Human-readable form Sequence of characters

-Integer 12345 stored as characters "1" "2" "3" "4" "5"

Use Reader and Writer and their subclasses

Writing text filesWriting text files

Use a PrintWriter -breaks up strings into individual characters -sends them one at a time to a FileWriter

Create a PrintWriter FileWriter writer = new FileWriter("output.txt");PrintWriter out = new PrintWriter(writer);

Use print and printlnout.println(29.95); out.println(new Rectangle(5,10,15,25));out.println("Hello, World!");

Use a BufferedReader -Reads a character at a time from a FileReader-Assembles the characters into a line and returns it

Use Integer.parseInt or Integer.parseDouble to convert the strings to numbers

Code FileReader reader = new FileReader ("input.txt");BufferedReader in = new BufferedReader(reader); String inputLine = in.ReadLine(); double x = Double.parseDouble(inputLine);

Basic streams, readers, and writers can process only _____________________. You need to combine them with other classes to process _______________ or _________________.

Basic streams, readers, and writers can process only _individual bytes or chars______. You need to combine them with other classes to process ___lines______ or ____objects______.

When writing text files, use ________________ class and the _____________________ methods.

When reading text files, use _______________ class and the ____________ method.

When writing text files, use _____PrintWriter______ class and the ____print/println__________ methods.

When reading text files, use _____BufferedReader________ class and the ___readLine______ method.

FileFile

File class describes disk files and directories Create a File object

File inputFile = new File("input.txt"); Some file methods

deleterenameToexists

Constructing a FileReader from a File object FileReader reader = new FileReader(inputFile) ;

A File object describes a ___________ or __________________.

A File object describes a _____file_______ or _______directory___________.

You can pass a File object to the constructor of a file ____________, _________, or stream.

You can pass a File object to the constructor of a file ____reader_________, ___writer________, or stream.

File ChooserFile Chooser

File ChoserFile Choser

Construct a file chooser object Call its showOpenDialog or showSaveDialog method Specify null or the user interface component over which to

pop up the dialog If the user chooses a file, these methods return

JFileChooser.APPROVE_OPTION If the user cancels the selection, these methods return

JFileChooser.CANCEL_OPTION If a file is chosen, use GetSelectedFile method to obtain a

File object describing the file

CodeCode

JFileChooser chooser = new JFileChooser();

FileReader in = null;

if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {

File selectedFile= chooser.getSelectedFile();

in = new FileReader(selectedFile);

}

The ______________________________ dialog lets users select a file by navigating directories.

The _JFileChooser__________ dialog lets users select a file by navigating directories.

Command LineCommand Line

Java MyProgram -d file.txt

class MyProgram {

public static void main(String[] args) { ...

// arg[0] == “-d”

// arg[1] == “file.txt”

}

}

When you launch a program from the command line, you can specify arguments after the program name. The program can access these strings by processing the ______________ parameter of the ___________ method.

When you launch a program from the command line, you can specify arguments after the program name. The program can access these strings by processing the _____”args”___ parameter of the ___main___ method.

Binary FormatBinary Format

More compact and efficient Integer 12345 stored as 00 00 48 57 Use InputStream and OutputStream and

their subclasses

File IOFile IO

We have seen character I/OSometimes, we want to have other data

types stored in file– It’s all just bits

Consider saving an arrayConsider 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 FileOpen the File

private void saveArray() {

try {


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 arrayWrite 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 fileOpen the fileprivate void restoreArray() {

try {


BufferedReader in1 = null;

if (chooser.showOpenDialog(null) ==

JFileChooser.APPROVE_OPTION)

{


FileReader reader = new FileReader(selectedFile);

in1 = new BufferedReader(reader);

Read the arrayRead the arrayfor(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 FileText File

Text File

1.0

0.5

0.33333334

0.25

0.2

2.0

1.0

0.6666667

0.5

0.4

3.0 1.5 1.0 0.75 0.6 4.0 2.0 1.3333334 1.0 0.8 5.0 2.5 1.6666666 1.25 1.0

Byte by Byte Text file 303 Byte by Byte Text file 303 bytesbytes

0000000 1 . 0 \r \n 0 . 5 0000020 \r \n 0 . 3 3 3 3 3 3 3 40000040 \r \n 0 . 2 5 0000060 \r \n 0 . 2 \r \n 20000100 . 0 \r \n 1 . 0 0000120 \r \n 0 . 6 6 6 6 6 6 7 0000140 \r \n 0 . 5 \r0000160 \n 0 . 4 \r \n 3 . 0 0000200 \r \n 1 . 5 0000220 \r \n 1 . 0 \r \n 0 . 70000240 5 \r \n 0 . 6 0000260 \r \n 4 . 0 \r \n 20000300 . 0 \r \n 1 . 3 3 3 30000320 3 3 4 \r \n 1 . 0 0000340 \r \n 0 . 8 \r0000360 \n 5 . 0 \r \n 2 . 5 0000400 \r \n 1 . 6 6 6 6 6 6 60000420 \r \n 1 . 2 5 0000440 \r \n 1 . 0 \r \n0000457

Open the file (binary)Open the file (binary)

private void saveArray2() {

try {


DataOutputStream out1 = null;




FileOutputStream writer = new

FileOutputStream(selectedFile);

out1 = new DataOutputStream(writer);

Write the fileWrite the file



out1.writeFloat(a[i][j]);

System.out.println(" " + a[i][j]);

}

writer.close();

}


}

}

Open the fileOpen the fileprivate void restoreArray2() {

try {


DataInputStream in1 = null;




FileInputStream reader = new FileInputStream(selectedFile);

in1 = new DataInputStream(reader);

Read the fileRead the file



a[i][j] = in1.readFloat();

}

reader.close();

}


repaint();

}

Same data - 100 BytesSame data - 100 Bytes

0000000 1.0000000e+00 5.0000000e-01 3.3333334e-01 2.5000000e-01

0000020 2.0000000e-01 2.0000000e+00 1.0000000e+00 6.6666669e-01

0000040 5.0000000e-01 4.0000001e-01 3.0000000e+00 1.5000000e+00

0000060 1.0000000e+00 7.5000000e-01 6.0000002e-01 4.0000000e+00

0000100 2.0000000e+00 1.3333334e+00 1.0000000e+00 8.0000001e-01

0000120 5.0000000e+00 2.5000000e+00 1.6666666e+00 1.2500000e+00

0000140 1.0000000e+00

Data StreamsData 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)

Example CryptologyExample Cryptology

Ceasar Cipher

import java.io.FileReader;import java.io.FileWriter;import java.io.IOException;public class Crypt{ public static void main(String[] args){

boolean decrypt = false;int key = DEFAULT_KEY;FileReader infile = null;FileWriter outfile = null;

if (args.length < 2 || args.length > 4) usage();

try { for(int i = 0; i < args.length; i++){ if (args[i].substring(0, 1).equals("-")) // it is a command line option { String option = args[i].substring(1, 2); if (option.equals("d"))decrypt = true; else if (option.equals("k")){ key = Integer.parseInt (args[i].substring(2));if (key < 1 || key >= NLETTERS) usage();} }

else { if (infile == null)

infile = new FileReader(args[i]); else if (outfile == null)

outfile = new FileWriter(args[i]); }}

}catch(IOException e){ System.out.println("Error opening file"); System.exit(0);}

if (decrypt) key = NLETTERS - key;

try { encryptFile(infile, outfile, key); infile.close(); outfile.close();}catch(IOException e) { System.out.println("Error processing file"); System.exit(0);}

} /** Prints a message describing proper usage and exits. */ public static void usage() {

System.out.println ("Usage: java Crypt [-d] [-kn] infile outfile");System.exit(1);

}

public static char encrypt(char c, int k) {if ('a' <= c && c <= 'z') return (char)('a' + (c - 'a' + k) % NLETTERS);if ('A' <= c && c <= 'Z') return (char)('A' + (c - 'A' + k) % NLETTERS);return c;

} public static void encryptFile(FileReader in,

FileWriter out, int k) throws IOException { while (true) { int next = in.read(); if (next == -1)return; // end of file char c = (char)next; out.write(encrypt(c, k));}

}

public static final int DEFAULT_KEY = 3;

public static final int NLETTERS = 'z' - 'a' + 1;

}

Serializable ObjectsSerializable ObjectsWe can write whole objects to filesUsing object streamsmust implement “Serializable”

Use ______________________ to save and restore all instance fields of an object automatically.

Use ____object streams________ to save and restore all instance fields of an object automatically.

Objects saved to and object stream must belong to a class that implements the ______________________ interface.

Objects saved to and object stream must belong to a class that implements the ___Serializable_________ interface.

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 packagesimport 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 recordrecord = 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 recordrecord = (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();

}

0000000 254 355 \0 005 s r \0 \r A c c o u n t R

0000020 e c o r d G 346 306 343 235 233 005 \r 002 \0 004

0000040 I \0 007 a c c o u n t D \0 007 b a l

0000060 a n c e L \0 \t f i r s t N a m e

0000100 t \0 022 L j a v a / l a n g / S t

0000120 r i n g ; L \0 \b l a s t N a m e

0000140 q \0 ~ \0 001 x p \0 \0 \0 001 @ Y \0 \0 \0

0000160 \0 \0 \0 t \0 003 T e d t \0 \b P a w l

0000200 i c k i s q \0 ~ \0 \0 \0 \0 \0 002 @ 237

0000220 @ \0 \0 \0 \0 \0 t \0 004 A d a m t \0 005

0000240 F r a n k s q \0 ~ \0 \0 \0 \0 \0 003 A

0000260 c 022 320 \0 \0 \0 \0 t \0 003 J o e t \0 005

0000300 S c h m o

0000305

Streams CSC 171 FALL 2004 LECTURE 22. Make up exam Friday 12/3 11AM-12:10PM.

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Transcript of Streams CSC 171 FALL 2004 LECTURE 22. Make up exam Friday 12/3 11AM-12:10PM.