READING
Java Input and Output

*** THIS FIRST PART IS BASICALLY REVIEW ***
- input
  - any information needed by your program to complete execution
  - forms
    - graphical, e.g. popup dialog
    - clicking mouse
    - from file
    - from network connection
    - from devices (e.g. USB, camera, scanner, mike)
- output
  - information that the program must convey to the user
  - forms
    - what view on screen
    - print out created by a printer
    - sound from speakers
- I/O so far
  - input: BufferedReader plus System.in
  - output: PrintWriter via System.out
- errors while getting input
  - unexpected data format
    - e.g. letters instead of numbers
    - causes exception unless program designed to handle
- handle invalid input by only accepting valid input
  - not done by Java classes
    - gain flexibility at the cost of more complexity
- console input
  - any input entered in the console window
  - console window: black window automatically launched when CodeWarrior run
  - prompting the user
    - telling the user that s/he needs to provide input
    - formats
      - dialog box
      - program frame
      - console window
    - required if program needs to get info from user
      - don't count on blinking cursor
      - need to tell user what kind of input needed anyway
- java classes needed to successfully receive input from the user
  - mostly contained in the java.io package
  - major classes that we will use
    - to use, either
      - import java.io or
      - use the fully qualified names
    - java.io.InputStream
      - store info about the connection btw an input device and the program
    - java.io.InputStreamReader
      - translate data bytes received from an InputStream object into characters
    - java.io.BufferedReader
      - buffer/store input received from an InputStreamReader object
      - improves efficiency by reducing the number of times the program has to query the device for input
   - using these classes to get input
     - use BufferedReader instance method readLine
     - initialize the BufferedReader with an instance of java.io.Reader
       - InputStreamReader extends Reader, so we can just use InputStreamReader
       - initialize the InputStreamReader class with an instance of InputStream
         - java.lang.System class
           - automatically included with every class
           - includes an instance of InputStream connected to the keyboard
             - System.in
  - steps for console based user input
    - Use System.in to create an InputStreamReader object
    - Use InputStreamReader object ot create a BufferedReader object
    - Display a prompt to the user for the desired data
    - Use the BufferedReader object to read a line of text from the user
    - Use the input
  - readLine may throw a checked exception
    - must either catch the exception or add throws IOException to the declaration of the method that calls readLine
- integer input
  - readLine always returns a String
  - if a different type is desired, must parse (convert) the String to the desired type
  - parsing a String into an int
    - get a String of integer format via readLine
    - user the class method Integer.parseInt to parse the String
      - provide the String to parse as the sole argument
      - method returns the int to which the String is equivalent
      - if the String cannot be converted to an int, parseInt throws a NumberFormatException
  - Integer class is a wrapper class
    - many other wrapper classes
    - wrapper classes are used for
      - parsing
      - storing a primitive as an object
- console output
  - important alternative to graphical, which may not be readily supported by some environments
  - display a string of characters to some standard display device (usually the screen)
  - called console output b/c chars usually appear in the console window
  - System.out.print and System.out.println
    - System.out is an instance of the PrintStream class, which extends the Stream class
  - streams
    - instance of Stream class
      - store info needed to connect a program to an input or output device
    - Printer object adds functionality to output streams
      - PrintStream class
        - extends Printer
        - contains definitions for all of the versions of print and println
        - automatically created by java.lang.System when the application begins execution
          - public and static
          - InputStream: System.in
          - PrintStream: System.out, System.err
    - print and println work with any type of data
      - implemented as overloaded methods
      - use the toString conversion of whatever object is being printed
      - can overload the toString method for objects that you define so that printing them generates some logical output
  
*** THIS IS WHERE THE NEW STUFF BEGINS ***
- file input
  - reading files
  - attach a BufferedReader object to a FileReader instead of an InputStreamReader
  - assume text file with valid ASCII data
  - necessary classes
    - java.io.File
      - stores info about a file on a drive
      - constructor takes a String argument (the name of the file)
      - instance method exists returns whether that file exists, as a boolean
    - java.io.FileReader
      - translate file data bytes into a stream of characters
      - constructor takes a File object
      - close method closes the file stream
  - readLine returns null at the end of a file
    - must either propagate or catch associated IOException
  - string tokenizer
    - parse files to use as data (e.g., creating new objects)
    - delimiter: special character used to separate data fields
    - tokenizing: splitting a line of text into different parts
    - token: each piece of the split line
    - java.util.StringTokenizer class
      - constructor takes two objects, the first one a string representing the data to be parsed, and the second a string representint the delimiter
      - hasMoreTokens method determines whether there are more tokens to process
      - nextToken method returns the next token as a String
        - will throw a NoSuchElementException if called when no more tokens are left
      - countTokens method returns the number of remaining tokens
- file output
  - writing to a file 
  - file already exists  
    - behavior
      - overwrite
      - different file name
      - cancel
      - append
    - test for this: use File instance method exists()
 - classes
    - java.io.FileWriter
      - used to
        - open a file
        - connect an output stream to a file
      - constructor takes the name of the file to create , and a boolean of whether or not to append (overwrites if false)
    - java.io.PrintWriter
      - write strings of characters to a Writer object
      - constructor takes a Writer object and a boolean that says whether or not the data should be flushed (or force-written) to the file whenever println is used
      - print method takes a String to write to the file
        - this is buffered by default
        - means that it is not actually written to the file until the buffer is explictly flushed
      - flush method moves data from the buffer to the file
      - println method also takes a String to write to the file, but may automatically flush if requested initially in the constructor
      - close method required to ensure all of the data is saved properly
      - more efficient to wait to flush until done writing to buffer