Program to read bytes from file and convert to hex

Question

import java.io.*;

public class foo {

    public static void main(String[] args) {

        try {
            DataInputStream input = new DataInputStream(new FileInputStream(
                    "data.dat"));

            while (input.available() > 0) {

                String hex = Integer.toHexString(input.readByte()); //I think this is where the problem is

                System.out.print(hex + ' ');

            }

        } catch (IOException e) {
        }

    }
}

Output-

ffffff89 50 4e 47 d a 1a a 0 0 0 d 49 48 44 52 0 0 0... (continues)

The output is mostly correct. I can't figure out where these ffffffs are coming in my output. And also single single characters are missing their 0. eg. d should be displayed as 0D

Louis Wasserman · Accepted Answer · 2015-03-06 23:23:18Z

2

input.readByte() returns a signed byte; when the highest bit of that byte is 1, it is interpreted as a negative number, and Integer.toString sign-extends it to an int.

Instead of Integer.toString, use String.format("%02x", input.readByte() & 0xFF), which will interpret the byte as unsigned and force exactly two hexadecimal digits to be used.

answered Mar 6, 2015 at 23:23

Louis Wasserman

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