Problem in using offset value in streams

Question

hi friends,
I have been having this problem far few hours. I am unable to understand why this exception is comming, although I know the cause of exception as I have figured it out by now but unable to remove it.
here is a simple file copy program using character streams wrapped around Buffered streams.
   import java.io.*;
public class CopyBytes {
    public static void main(String[] args) throws IOException {
        BufferedReader in = null;
        BufferedWriter out = null;
        char []buff=new char[5];
        int offset=0,length=5;
        try {
            in = new BufferedReader(new FileReader("Factorial.java"));*
            out = new BufferedWriter(new FileWriter("outagain.java"));            
            while (true) {
                in.read(buff,offset,length);     //this line causing error
                out.write(buff,offset,length);
                offset+=length;
        } finally {
            if (in != null) {
                in.close();
            if (out != null) {
                out.close();
}when I ran the program I got following exception java.lang.IndexOutOfBountException
I know the exception is at commented line, but I am not sure wheather this is coming due to offset or length variable
by the way, first 5 characters from source file have been copied to destination file as I saw.
thanks in advance

Answer 1

san_4u wrote:
how can I skip offset variable as this method must pass one char[] and two int variables.
would you please explain how these three parameters are being used. I have read it many times but still unable to understand the use of offset and length variables.For the read method, the offset parameter specifies at which index of buff to start writing data.
For the write method, the offset parameter specifies from which index of buff to start reading data.
Since you are using buff as temporary buffer only, you can always read stuff into buff at its beginning (i.e. index 0).
Of course, when writing data to the stream from buff, you should write the data previously stored. So, you should (obviously) use the same offset for writing to the stream as you previously used when reading from the stream. To be able to write exactly the data you previously read, you also need to know how many chars were read and stored in buff. Luckily, that is exactly what the return value of read does tell you (with -1 being a special flag for "no more data available").
Hope you can figure it out now.