Computer Science Canada

Java File Input (Character by Character)
Author:  morningpost [ Tue Jan 25, 2011 9:05 pm ]
Post subject:  Java File Input (Character by Character)
Hi there,

I just need to know how to read in from a text file character by character in Java.

I've tried using Scanner, InputStreamReader, DataInputStream, FileInputStream ... but I'm obviously going wrong somewhere. I just can't seem to be able to read in from the file character by character. The file is supposed to be a maze, with the first two numbers representing # of columns and # of rows. I want to read in character by character so I can place the characters into a 2D array in my program.

The textfile looks something like this (legend: '#' - wall, '.' - open space, 'o' - start, '*' - finish):

7 4
#######
# . . . #o#
# *#. . . #
#######

^ So, these are the types of characters I want to read in one by one Smile

If someone could help with this, that'd be great! Thanks! Very Happy
Author:  Tony [ Tue Jan 25, 2011 9:19 pm ]
Post subject:  RE:Java File Input (Character by Character)
How did you try using Scanner?

http://download.oracle.com/javase/6/docs/api/java/util/Scanner.html
Author:  morningpost [ Tue Jan 25, 2011 9:27 pm ]
Post subject:  Re: RE:Java File Input (Character by Character)
Tony @ Tue Jan 25, 2011 9:19 pm wrote:
How did you try using Scanner?

http://download.oracle.com/javase/6/docs/api/java/util/Scanner.html


I tried using the Scanner this way, but it won't read in character by character ...

File file = new File("maze1.txt");
try {
s = new Scanner(file);

int columns = s.nextInt();
int rows = s.nextInt();
String grid = new String[rows][columns];

while (s.hasNext()) {
int r = 0;
int col = 0;
String square = s.next();
grid[r][col] = square;

r++;
col++;
}
}catch (FileNotFoundException e) {
System.out.println("File cannot be found! " + e);
}
Author:  Tony [ Tue Jan 25, 2011 9:40 pm ]
Post subject:  RE:Java File Input (Character by Character)
What does #next() return..?
http://download.oracle.com/javase/6/docs/api/java/util/Scanner.html#next()

code:

String grid = new String[rows][columns];

Wait, what does this mean?
Author:  RandomLetters [ Tue Jan 25, 2011 9:43 pm ]
Post subject:  RE:Java File Input (Character by Character)
You can use toCharArray() method to convert string to an array of characters.
Author:  morningpost [ Tue Jan 25, 2011 9:49 pm ]
Post subject:  Re: RE:Java File Input (Character by Character)
Tony @ Tue Jan 25, 2011 9:40 pm wrote:
What does #next() return..?
http://download.oracle.com/javase/6/docs/api/java/util/Scanner.html#next()

code:

String grid = new String[rows][columns];

Wait, what does this mean?


next () returns the entire first row and then nothing else :\

oh, sorry. It's suppose to be String [][] grid = new String[rows][columns]. My mistake.
Author:  Tony [ Tue Jan 25, 2011 9:53 pm ]
Post subject:  Re: RE:Java File Input (Character by Character)
morningpost @ Tue Jan 25, 2011 9:49 pm wrote:
next () returns the entire first row and then nothing else :\

Yup, sounds like that's not the method that you are looking for. Find one that returns the type that you want.
Author:  ProgrammingFun [ Tue Jan 25, 2011 10:21 pm ]
Post subject:  RE:Java File Input (Character by Character)
Why don't you use BufferedReader to read one line at a time. This line can be saved in a String from which you can use .charAt() to extract characters?
Author:  Tony [ Tue Jan 25, 2011 10:38 pm ]
Post subject:  RE:Java File Input (Character by Character)
Or use a Scanner to scan for the next character token and use that directly.
Author:  RandomLetters [ Tue Jan 25, 2011 11:24 pm ]
Post subject:  Re: RE:Java File Input (Character by Character)
Tony @ Tue Jan 25, 2011 10:38 pm wrote:
Or use a Scanner to scan for the next character token and use that directly.


How do you do that? next() Set delimiter to ""? I could not find a nextChar() method or similar, which is interesting (so there must be an obvious way)

:


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