chapter 10 ch 1 – introduction to computers and java streams and file io 1
TRANSCRIPT
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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>