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Chapter 10 Ch 1 – Introduction to Computers and Java Streams and File IO 1 Chapter 10 10.1 File IO Overview 10.2 Text-File IO 10.3 File Techniques 10.6 Graphics Supplement 2 10.1 File IO Overview 3 A stream is a stream is a stream All IO can be viewed as a stream of data 4 An Input stream delivers data to your program Streaming data 5 An Output stream accepts data from your program Streaming data 6 A file could be treated as text or binary All data is binary at the end of the day 7 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 8 A binary file manipulates the binary data 12345 -4027 8 Each data item uses the same number of bytes (4 for ints) 9 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 10 10.2 Text-File IO 11 There are four steps in using file IO 1 Open the file stream 2 Test the Connection 3 Perform the IO 4 Close the stream 12 (1) Open the file stream // Reading Scanner fin = null; try { fin = new Scanner(new File(filename)); } // Writing PrintWriter 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)); } 13 (2) Test the Connection catch (FileNotFoundException e) { System.err.println("Error opening file " + filename); System.exit(1); } 14 (3) Perform the IO // Reading while (fin.hasNextLine()) { String line = fin.nextLine(); // process the line ... } // Writing fout.println("Write some output"); ... 15 (4) Close the Stream // Reading fin.close(); // Writing fout.close(); 16 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 17 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 18 Application Deconstructed <FileOutput.java> 19 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 20 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 21 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 22 10.3 File Techniques 23 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. 24 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()); 25 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 26 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 27 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 28 Application Deconstructed <FileClass.java> // Let's test some File methods. ... System.out.println("Filename: " + file.getName()); ... }// end main() }// end FileClass 29 Application Deconstructed <FileClass.java> // Let's test some File methods. ... System.out.println("File path: " + file.getPath()); ... }// end main() }// end FileClass 30 Application Deconstructed <FileClass.java> // Let's test some File methods. ... System.out.println("File absolute path: " + file.getAbsolutePath()); ... }// end main() }// end FileClass 31 Application Deconstructed <FileClass.java> // Let's test some File methods. ... System.out.println("File length: " + file.length() + " bytes"); }// end main() }// end FileClass 32 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 33 Application Deconstructed <FileClass.java> 34 Application Deconstructed <CSVFile.java> package csvfile; import import import import java.io.PrintWriter; java.io.File; java.io.FileNotFoundException; java.util.Scanner; public class CSVFile { public static void main(String[] args) { Scanner fin = null; PrintWriter fout = null; String filename = "csv.txt"; 35 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 36 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 37 Application Deconstructed <CSVFile.java> fin.close(); fout.close(); System.out.println(filename + " was read and " + "csvout.txt was written."); }// end main() }// end CSVFile 38 Application Deconstructed <CSVFile.java> 39 Recap Use a File object for useful file information A csv file requires special handling (for now anyway) 40 10.6 Graphics Supplement 41 Application Deconstructed <FileFrame.java> package fileframe; import import import import import import javax.swing.JFrame; javax.swing.JTextArea; java.awt.Container; java.util.Scanner; java.io.File; 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() 42 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() 43 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 44 Application Deconstructed <FileFrame.java> 45