LECTURE
12 NOVEMBER 2004

ASSIGNMENTS
Today 11:58 PM CodeLab #10
Mon 11/22 Assignment 4

STRING TOKENIZER

Why?
- what to do with the file once reading it
- may want to interpret the data in special ways
- very common way: databases or spreadsheets -- creating new objects from the data in the file

What?
- delimiter: special character used to separate data fields
- tokenizing
  - splitting a line of text into different parts (tokens)
  - throws away the delimiter

How?
- java.util.StringTokenizer class
- constructor
  - arguments
    1. String of the data to be parsed
    2. String of all delimiters
       - (optional) default delimiters: space, tab, newline, return
- 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

Example:
  System.out.println("Enter a line with integers: ");
  String input = stdin.readLine();

  StringTokenizer st;
  String delims = " ,;\t";
  st = new StringTokenizer( input, delims );
  while ( st.hasMoreTokens() ) 
  {
    int n = Integer.parseInt(st.nextToken());
    System.out.println(n);
  }

FILE OUTPUT

What?
- writing to a file

What?
- if the file already exists
How?
- File instance method exists()
Options?
- overwrite
- different file name
- cancel
- append

How?
- similar to BufferedReader, but in the opposite direction
- output stream: stream of data to output from your program

What?
- open a file
- connect an output stream to a file
How?
- java.io.FileWriter
- constructor takes the name of the file to create , and a boolean of whether or not to append (overwrites if false) 

What?
- write strings of characters to a Writer object
- use a FileWriter to write to a file
How?
- java.io.PrintWriter
- 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

Example:
        // Create a FileWriter attached to a file named "out.txt".
        // The second parameter sets whether or not new data
        // will be appended to the end of the file or the beginning.
        // false means that this file will be overwritten.
        java.io.FileWriter fw = new java.io.FileWriter( "out.txt", false );
    
        // Create a PrintWriter that automatically flushes data
        // to the output file whenever the println method is used.
        java.io.PrintWriter pw = new java.io.PrintWriter( fw, true );

        // Buffer some data to write to the file (doesn't actually write until flush)
        pw.print( "Some test data that will be written when flush is called.");
        
        // Flush all buffered data to the file.
        pw.flush();

        // Write some data and automatically flush it to the file.
        pw.println( data );

        // Close the PrintWriter for added safety.
        pw.close();

FILE IO CUMULATIVE EXAMPLE

    - java.io.File: additional useful methods
      - instance method isFile returns whether or not the object is a file (as opposed to being a directory)
      - instance method isDirectroy returns whether or not the object is a directory
      - instance method canRead returns whether or not the program can read the file (it might not have security permissions)
      - instance method canWrite returns whether or not the program can write the file
      - instance method ready() returns whether or not there are still characters in the file to be read