21 Jan 2008

present:  IP, UK, WO, RR

Commands learnt:

HOw to read in data from a file.dat:

1) we can define an imagined channel between a java program and a file on the same directory
2) use Scanner to define the name of the channel
   if the direction is in, then two commands can be used easily:
   
   	i) boolean xxxx.hasNextLine();
   	ii) we can read the next line by xxxx.nextLine();
   	
   		our guess is:  there is a pointer/marker which will moves to a new line (next line)
		each time after you call xxxx.nextLine();
3) Note we need to use 	'throws Exception'



How to write to a file.dat: 

1) we still need to use 'throws Exception'
2) similart to Scanner, we use PrintStream

	PrintStream outChannle = new PrintStream(new FileOutputStream("fileX"));
	
	// where fileX can be a file to be created, i.e. fileX does not have to be in the current directory already.
	
3) we use xxxx.print();  and xxxx.println() to write the data into the file.
4) note: fileX can be in a existing directory, this command cannot create a new directory.
5) note: fileX will be cleared before writing to it.





Question:
1) Given a file :   "testfile.dat", we want to write a method to change the first line to "HELLO":

	Algorithm I
	1. define a inChannel, read in the data
	2) define a outChannel and write out "HELLO" to the first line of the same file
	
	Algorithm II
	1. define a outChannel and write out "HELLO" to the first line of the same file
	
2) Given a file, we want to first display the content, then remove the second line of the file.

	Algorithm:
	1) define a inChannel, and read the data, then System.out.println();
	2) define a outChannel, and find the location, i.e the second line, then write "";  ??
	
	
Question:

How can we update certain line of an existing file?

3) Write a method to print a interesting pattern to a text tile.txt