Question

According to Java documentation, the readlimit parameter of the mark method in the Class InputStream server for set “the maximum limit of bytes that can be read before the mark position becomes invalid.”.
I have a file named sample.txt whose content is “hello”. And i wrote this code:

import java.io.*;
public class InputStream{
 public static void main (String[] args) throws IOException {
  InputStream reader = new FileInputStream("sample.txt");
  BufferedInputStream bis = new BufferedInputStream(reader);
  bis.mark(1);
  bis.read();
  bis.read();
  bis.read();
  bis.read();
  bis.reset();
  System.out.println((char)bis.read());
 }
}

The output is “h”. But if i after the mark method read more than one bytes, shouldn’t i get an error for the invalid reset method call?

Answer 1

I would put this down to documentation error.

The non-parameter doc for BufferedInputStream is “See the general contract of the mark method of InputStream,” which to me indicates that BufferedInputStream does not behave differently, parameter doc notwithstanding.

And the general contract, as specified by InputStream, is

The readlimit arguments tells this input stream to allow that many bytes to be read before the mark position gets invalidated […] the stream is not required to remember any data at all if more than readlimit bytes are read from the stream

In other words, readlimit is a suggestion; the stream is free to under-promise and over-deliver.