Question about Java File Reader.

Question

Hello. I'm having some problems with the FileReader class.

How do I specify an offset in the lines it goes through, and how do I tell it when to stop? Let's say I want it to go through each line in a .txt file, but only lines 100-200 and then stop?

How would I do this? Right now I'm using ReadLine() but I don't think there's a way to specify offset with that.

Any fast help is VERY appreciated. Thanks.

Answer 1

Read all the lines but use another variable to count which line you are on. Call continue if you are on a line that you don't want to process (say, before the 100th line) and break when you will not want to process any more lines (after the 200th line).

Answer 2

1. You can't. FileReader reads a character at a time or a line at a time. Obviously you can write your own code extending or wrapping it to skip to the unneeded lines.

2. An aside: Be CAREFUL using FileReader or FileWriter - they use the default LOCALE character set. If you want to force a character set use OutputStreamWriter or InputStreamReader. Example

Writer w = new FileWriter(file) can be replaced by Writer w = new OutputStreamWriter(new FileOutputStream(file),"UTF-8"); <=== see how I can set the character set.

1. An alternative: If you have FIXED-WIDTH text, then look at RandomAccessFile which lets you seek to any position. This doesn't help you much unless you have fixed width text or an index to skip to a line. But it is handy :)

Answer 3

There is not a way to tell the reader to only read certain lines, you can just use a counter to do it.

try { 
    BufferedReader in = new BufferedReader(new FileReader("infilename")); 
    String str; 
    int lineNumber = 0;

    while ((str = in.readLine()) != null) { 
        lineNumber++;

        if (lineNumber >= 100 && lineNumber <= 200) {
            System.out.println("Line " + lineNumber + ": " + str);
        }
    } 

    in.close(); 
} catch (IOException e) { } 

Answer 4

BufferedReader in = new BufferedReader(new FileReader("foo.in"));
for(int i=0;i<100;i++,in.readLine()){}
String line101 = in.readLine();