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Chapter 10

Ch 1 – Introduction toComputers and Java

Streams and File IO

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Chapter 10

10.1 File IO Overview

10.2 Text-File IO

10.3 File Techniques

10.6 Graphics Supplement

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10.1File IO

Overview

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A stream is a stream is a stream

All IO can be viewed as a stream of data

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An Input stream delivers data toyour program

Streaming data

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An Output stream accepts data from your program

Streaming data

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A file could be treated astext or binary

All data is binary at the end of the day

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A text file treats the binary data as characters

1 2 3 4 5 - 4 0 2 7 8

Each digit uses 1 (ASCII) or 2 (Unicode) bytes

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A binary file manipulates the binary data

12345 -4027 8

Each data item uses the same number of bytes (4 for ints)

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Recap

A program reads data from an input stream

A program writes data to an output stream

A text file interprets its binary data as text

A binary file deals with the binary data itself

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10.2Text-File IO

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There are four steps in using file IO

Open the file stream1

Test the Connection2

Perform the IO3

Close the stream4

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(1) Open the file stream// ReadingScanner fin = null;

try { fin = new Scanner(new File(filename));}

// WritingPrintWriter fout = null;

try { // Create empty file fout = new PrintWriter(filename); // or fout = new PrintWriter(new FileOutputStream(filename, false));

// Append to the file fapp = new PrintWriter(new FileOutputStream(filename, true));}

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(2) Test the Connection

catch (FileNotFoundException e) { System.err.println("Error opening file " + filename); System.exit(1);}

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(3) Perform the IO

// Readingwhile (fin.hasNextLine()) { String line = fin.nextLine(); // process the line ...}

// Writingfout.println("Write some output");...

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(4) Close the Stream

// Readingfin.close();

// Writingfout.close();

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Application Deconstructed<FileOutput.java>

package fileoutput;

import java.io.PrintWriter;import java.io.FileNotFoundException;

public class FileOutput { public static void main(String[] args) { PrintWriter fout = null; String filename = "fileOutput.txt"; // Open and test the output stream. try { fout = new PrintWriter(filename); } catch (FileNotFoundException e) { System.err.println("Error opening the file " + filename); System.exit(1); }// end try

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Application Deconstructed<FileOutput.java>

// Perform some IO. for (int line = 1; line <= 5; line++) { fout.println(line + ": " + "This is just a line"); } // Close the stream. fout.close(); System.out.println("File " + filename + " was created successfully."); }// end main()} // end FileOutput

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Application Deconstructed<FileOutput.java>

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Application Deconstructed<FileInput.java>

package fileinput;

import java.util.Scanner;import java.io.File;import java.io.FileNotFoundException;

public class FileInput { public static void main(String[] args) { String filename = "fileOutput.txt"; Scanner fin = null;

// Open and test the stream. try { fin = new Scanner(new File(filename)); } catch (FileNotFoundException e) { System.err.println(e); System.exit(1); }// end try

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Application Deconstructed<FileInput.java>

// Perform the IO. while (fin.hasNext()) { int lineNumber = Integer.parseInt( fin.next().replace(":", "")); String lineText = fin.nextLine(); System.out.println(lineText + lineNumber); }// end while // Close the stream. fin.close(); }// end main()}// end FileInput

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Recap

Open the file stream first in a try block

Catch any errors that occur during opening

Perform the IO

Close the stream as soon as IO is finished

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10.3File

Techniques

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The File class offers useful functionality

public boolean canRead() // Can program read from the file?

public boolean canWrite() // Can program write to the file?

public boolean delete() // Was file detected?

public boolean exists() // Does the file exist?

String getName() // Get file's name.

String getPath() // Get file's path.

public long length() // Get file's path.

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Application Deconstructed<FileClass.java>

package fileclass;

import java.io.File;import java.util.Scanner;

public class FileClass {

public static void main(String[] args) { Scanner keyboard = new Scanner(System.in); File file = null; // Ask the user for the file. System.out.print("Enter the filename: "); file = new File(keyboard.nextLine());

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Application Deconstructed<FileClass.java>

// Let's test some File methods. System.out.println(""); System.out.println("Does file exist? " + String.valueOf(file.exists())); ... }// end main()}// end FileClass

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Application Deconstructed<FileClass.java>

// Let's test some File methods. ... System.out.println("Can file be read? " + String.valueOf(file.canRead())); ... }// end main()}// end FileClass

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Application Deconstructed<FileClass.java>

// Let's test some File methods. ... System.out.println("Can file be written? " + String.valueOf(file.canWrite())); ... }// end main()}// end FileClass

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Application Deconstructed<FileClass.java>

// Let's test some File methods. ... System.out.println("Filename: " + file.getName()); ... }// end main()}// end FileClass

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Application Deconstructed<FileClass.java>

// Let's test some File methods. ... System.out.println("File path: " + file.getPath()); ... }// end main()}// end FileClass

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Application Deconstructed<FileClass.java>

// Let's test some File methods. ... System.out.println("File absolute path: " + file.getAbsolutePath()); ... }// end main()}// end FileClass

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Application Deconstructed<FileClass.java>

// Let's test some File methods. ... System.out.println("File length: " + file.length() + " bytes"); }// end main()}// end FileClass

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Application Deconstructed<FileClass.java>

// Let's test some File methods. System.out.println(""); System.out.println("Does file exist? " + String.valueOf(file.exists())); System.out.println("Can file be read? " + String.valueOf(file.canRead())); System.out.println("Can file be written? " + String.valueOf(file.canWrite())); System.out.println("Filename: " + file.getName()); System.out.println("File path: " + file.getPath()); System.out.println("File absolute path: " + file.getAbsolutePath()); System.out.println("File length: " + file.length() + " bytes"); }// end main()}// end FileClass

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Application Deconstructed<FileClass.java>

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Application Deconstructed<CSVFile.java>

package csvfile;

import java.io.PrintWriter;import java.io.File;import java.io.FileNotFoundException;import java.util.Scanner;

public class CSVFile {

public static void main(String[] args) { Scanner fin = null; PrintWriter fout = null; String filename = "csv.txt";

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Application Deconstructed<CSVFile.java>

try { fin = new Scanner(new File(filename)); fout = new PrintWriter("csvout.txt"); } catch (FileNotFoundException e) { System.err.println(e); System.exit(1); }// end try

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Application Deconstructed<CSVFile.java>

String line = null; int pos;

// Read from the input file and write to output file. while (fin.hasNextLine()) { line = fin.nextLine(); // Write the record number. pos = line.indexOf(","); fout.print(line.substring(0, pos) + ":"); line = line.substring(pos + 1); // Write the first name. pos = line.indexOf(","); fout.print(line.subSequence(0, pos) + ":"); line = line.substring(pos + 1); // Write the last name. fout.println(line); }// end while

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Application Deconstructed<CSVFile.java>

fin.close(); fout.close(); System.out.println(filename + " was read and " + "csvout.txt was written."); }// end main()}// end CSVFile

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Application Deconstructed<CSVFile.java>

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Recap

Use a File object for useful file information

A csv file requires special handling (for now anyway)

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10.6Graphics

Supplement

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Application Deconstructed<FileFrame.java>

package fileframe;

import javax.swing.JFrame;import javax.swing.JTextArea;import java.awt.Container;import java.util.Scanner;import java.io.File;import java.io.FileNotFoundException;

public class FileFrame extends JFrame { JTextArea contentsTextArea; public static void main(String[] args) { FileFrame frame = new FileFrame(); frame.setSize(600, 500); frame.setTitle("File Viewer :: fileOutput.txt"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); }// end main()

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Application Deconstructed<FileFrame.java>

// Constructor. public FileFrame() { initComponents(); }// end FileFrame() private void initComponents() { // Create the TextArea. contentsTextArea = new JTextArea(); Container contentPane = getContentPane(); // Add the control to the content pane. contentsTextArea.setSize(590, 470); contentPane.add(contentsTextArea); // Load the text file contents into the TextArea. LoadTextAreaWithFile("fileOutput.txt"); }// end initComponents()

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Application Deconstructed<FileFrame.java>

private void LoadTextAreaWithFile(String filename) { Scanner fin = null; try { fin = new Scanner(new File(filename)); } catch (FileNotFoundException e) { System.err.println(e); System.exit(1); }// end try while (fin.hasNextLine()) { contentsTextArea.append(fin.nextLine() + "\n"); }// end while fin.close(); }// end LoadTextAreaWithFile()}// end FileFrame

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Application Deconstructed<FileFrame.java>