1. CSSE221 Section 2

2.  Using JFileChooser to ease use of file I/O in GUI programs  Review of text-based file I/O  Streams/Readers/Writers  Using the File class to manage file systems  Object-based, compressed, and byte- based file I/O

3.  When coding a GUI, JAVA provides a JFileChooser in swing. JFileChooser is very customizable, with features such as filters for file extensions when opening and saving.  Another advantage to JFileChooser is the ability to have it filter the list of files to only a few. If you wanted to pass only.txt files into a program, you would use a FileFilter or FilenameFilter with the JFileChooser.

4. public static void main(String[] args) { JFileChooser jfc = new JFileChooser(); int returnVal = jfc.showOpenDialog(jfc); //Here to make sure a valid file is selected if (returnVal == JFileChooser.APPROVE_OPTION) { String inputFile = jfc.getSelectedFile().toString(); int n = 1; // prefix-length int maxWordsGen = 100; int maxCharsPerLine = 20; Markov m = new Markov(inputFile, n, maxWordsGen, maxCharsPerLine); } else{ System.out.println("Failed because no file was selected"); }  Markov will not work outright with this, as a few changes will need to be made to how Markov interprets file location, but the correct file will be selected.

5.  The FileFilter Interface requires the method: public boolean accept(File f)  To use a FileFilter with the JFileChooser from the last example, the following code would be placed after JFileChooser jfc was initialized: jfc.addChoosableFileFilter(new FileFilter(){…}); jfc.setAcceptAllFileFilterUsed(false);

6. Basic text-based file I/O review: File name=new File(“file.txt”); BufferedReader fileIn=null; try{ fileIn=new BufferedReader(new FileReader(name)); //read your data in }catch(IOException e){ //error handling }finally{ fileIn.close(); }

7.  Streams are the basis of all I/O in Java (terminal, web sockets, files, etc…).  A Stream is created for EITHER input or output, NOT both  The Reader and Writer classes we commonly use are extension of the Stream classes  The Scanner used with Markov is an example of a “simplified” input class, though it does not directly extend a Stream  The Stream concept is important, and we will revisit it later when discussing other types of I/O

8.  Buffered Classes: a Buffered class extends its lower counterpart (i.e. BufferedReader extends FileReader).  Buffering allows reading of more than a single “piece” of data at a time.  Whether or not you want to use Buffered classes is largely a design/functionality decision

9.  Correct order of instantiation must be followed  A Stream/Reader/Writer must be initialized inside a try/catch/finally block that catches an IOException.  The “outermost” Stream/Reader/Writer needs to be declared and set to null BEFORE the try/catch block  A Stream/Reader/Writer needs to be closed (preferably in the finally block), or else: Files written will not “finalize” and will not appear correctly. Files read may be “locked” into the program, and not be available elsewhere. Only a limited number of Streams can be open at once.

10.  The File class creates an object representing a file on the user’s system  Constructors: new File(String name); new File(File parent, String suffix); new File(File parent, File suffix);  Useful methods: exists() createNewFile() isDirectory() length()* lastModified()* list() listFiles()

11.  Review of text-based file I/O  Using the File class to define and organize files  Using the File class to gather data about and modify files

12.  Take the text from textFile.txt, and append it to the end of data/existingData.txt  Next, move the textFile.txt file to the data/newData directory as newFile.dat (HINT: the older textFile.txt may be removed in the process)  BONUS: within data/newData, create a directory named for each line of data/existingData.txt This exercise builds off the file structure already created in the fileSystemExample() and textIOExample() so keep in mind the location and state of the files after that code is run !!

13.  Saving/retrieving data for use in a program can become complicated, using Object I/O can save you from having to convert/organize all your data for text- based I/O  Uses ObjectOuputStream and ObjectInputStream classes  Objects may be written to a file as long as they implement the Serializable interface.  See example code in full version of Demo

14.  Compressed I/O allows you to write data to.zip files which can save space and make archiving easier.  Uses GZIPOutputStream and GZIPInputStream, and is implemented after the basic/buffered level, but before the specific level.  See example code in full version of Demo

15.  Byte-based I/O allows Java to handle reading/writing of files that are neither text- based nor object based.  Uses DataInputStream and DataOutputStream  NOTE: unlike text-based and object- based, information read into the program can only be worked with if the decoding is known.  Again, see example code in full version of Demo

16.  BufferedInputStream read(); close();  BufferedReader read(); readLine(); close();  ObjectInputStream readObject(); close();  DataInputStream readFully(byte[] b);  BufferedOutputStream write();  BufferedWriter write(); newLine(); close();  ObjectOutputStream writeObject(); close();  DataOutputStream write();