1. Java Review 2

2. The Agenda The following topics were highlighted to me as issues: –File IO (Rem) –Wrappers (Rem) –Interfaces (Rem) –Asymptotic Notation (Elani)

3. File Input / Output File I/O is stream based! –To read data from a file, we must create an instance of the FileInputStream class. –To write data to a file, we must create an instance of the FileOutputStream class. In Java, specific files are represented as instances of the File class. –E.g. File myFile = new File(“c:\\myfile.txt”); here myFile references a File object that represents the file myfile.txt on my c drive. –The File class is part of the java.io package. i.e we must put the following at the top of our code: import java.io.File;

4. Reading from a file To read from a file: –Create an instance of the File class that references the file. i.e. File file = new File(“c:\\example.txt”); –Create a FileInputStream for that file. i.e. FileInputStream fin = new FileInputStream(file); –Create the InputStreamReader and BufferedReader classes. i.e. InputStreamReader isr = new InputStreamReader(fin); BufferedReader in = new BufferedReader(isr); –Read from the file. i.e. String line = in.readLine();

5. Example – Reading a User Specified File import java.io.*; class MyProgram { public static void main(String[] args) { BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); String line = null; System.out.println("Input a filename:" ); try { line = in.readLine(); } catch (IOException ie) { System.out.println("Exception caught: " + ie); } File f = new File(line); try { FileInputStream fin = new FileInputStream(f); in = new BufferedReader(new InputStreamReader(fin)); while ((line = in.readLine()) != null) { System.out.println(line); } } catch (FileNotFoundException fnfe) { System.out.println("File " + f.getAbsolutePath() + " not found"); } catch (IOException ie) { System.out.println("IO Exception caught: " + ie); }

6. Writing to a File To write data to a file: –Create an instance of the File class that references the file. i.e. File file = new File(“c:\\example.txt”); –Create a FileOutputStream for that file. i.e. FileOutputStream fout = new FileOutputStream(file); –Create the PrintWriter class. i.e. PrintWriter out = new PrintWriter(fout); –Write data to the file. i.e. o ut.println(“data”);

7. Writing Data to a File import java.io.*; class MyProgram { public static String readUserInput() { String line = null; BufferedReader in = new BufferedReader( new InputStreamReader(System.in)); try { line = in.readLine(); } catch (IOException ie) { System.out.println("Exception caught: " + ie); } return line; }

8. Writing Data to a File public static void main(String[] args) { System.out.println("Input a filename:" ); String line = readUserInput(); File f = new File(line); try { FileOutputStream fout = new FileOutputStream(f); PrintWriter out = new PrintWriter(fout); System.out.println("Enter the data:"); line = readUserInput(); while (!line.equals("EOF")) { out.println(line); line = readUserInput(); } out.close(); } catch (FileNotFoundException fnfe) { System.out.println("File " + f.getAbsolutePath() + " not found"); } catch (IOException ie) { System.out.println("IO Exception caught: " + ie); }