File I/O

Reading a text file using BufferedReader

• use BufferedReader to read a text file line by line.
• use .ready() in the while test. Don't test for EOF condition.
• use .readLine() to read the entire line into a String.
• Buffered Reader is more efficient (faster) than Scanner because it does not convert the Strings to number etc.
• On very large files you will see a significant speedup using BufferedReader over Scanner.

• 
  	BufferedReader infile = new BufferedReader( new FileReader(args[0]) );
  	while ( infile.ready() )
  	{
  		String line = infile.readLine();
  	}
  	infile.close();

Reading a text file using Scanner

• use Scanner to read individual tokens (as opposed to reading the entire line at a time).
• You can however, easily read an entire line at a time with Scanner using .nextLine(). It's just not as efficient as BufferedReader on large files
• Scanner reads tokens from a file and converts them to numbers or other types exactly as it does from the keyboard.
• use the same Scanner methods next(), nextDouble(), nextInt() etc just like you do for the keyboard.
• Assume your input file looks like this:

  
  hoffmant  3.141  1991  true
  janedoe 4.00  2010  false

  and you want to read these values from the file into variables in your program, you can do it as below if you are sure the values are formatted correctly.

  Scanner infile = new Scanner (new File( args[0] ));
  while (infile.hasNext() )  // while there is something left in the file to read (we ASSUME the file is formatted correctly)
  {
  	String name = infile.next(); // grabs the next token treats as String
  	double gpa = infile.nextDouble();
  	double yrGrad = infile.nextInt();
  	boolean faculty = infile.nextBoolean();
  }
  infile.close();

Writing a text using PrintWriter

• Use PrintWriter to write to a text file. Use ..print() and .println() just the way you write to the screen.

  
  	PrintWriter outfile = new PrintWriter( new File(args[0]) );
  	int x = 235;
  	outfile.println("Hello World");
  	outfile.println("The value of x is: " + x );
  	outfile.close();

• Use Scanner to read values other than entire lines of text from a file. If the text file contains various types of data then use the Scanner just as you would to read from the keyboard, but instantiate the Scanner on a text file instead of the System.in device (keyboard). Assume your input file looks like this:

  
  hoffmant  3.141  1991  true
  janedoe 4.00  2010  false

  and you want to read these values from the file into variables in your program.

  Scanner infile = new Scanner (new File( args[0] ));
  while (infile.hasNext() )  // while there is something left in the file to read (we ASSUME the file is formatted correctly)
  {
  	String name = infile.next(); // grabs the next token and leaves it as a String
  	double gpa = infile.nextDouble(); // grabs the next token and converts to double
  	int yrGrad = infile.nextInt(); // grabs the next token and converts to int
  	boolean faculty = infile.nextBoolean(); // grabs the next token and converts to boolean
  }
  infile.close();