how to convert hex to byte for the following program?

public static String asHex (byte buf[]) {
    StringBuffer strbuf = new StringBuffer(buf.length * 2);
    int i;

    for (i = 0; i < buf.length; i++) {
        if (((int) buf[i] & 0xff) < 0x10)
            strbuf.append("0");

        strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
    }

    return strbuf.toString();
}

From stackoverflow

• To get a hexadecimal string representation of a byte array, you could use String.format() with the %X format specifier:

  public static String asHex(byte buf[]) 
  {
      StringBuffer strbuf = new StringBuffer(buf.length * 2);
  
      for (byte b : buf)
         strbuf.append(String.format("%02X", b));
  
      return strbuf.toString();
  }
  

  The following method gives the inverse operation, returning a byte array representation of a hexadecimal string. It uses Byte.parseByte() and some bit shifting to get two characters in one byte:

  public static byte[] asBytes(String str)
  {
      if ((str.length() % 2) == 1) str = "0" + str; // pad leading 0 if needed
      byte[] buf = new byte[str.length() / 2];
      int i = 0;
  
      for (char c : str.toCharArray())
      {
          byte b = Byte.parseByte(String.valueOf(c), 16);
          buf[i/2] |= (b << (((i % 2) == 0) ? 4 : 0));
          i++;
      }
  
      return buf;
  }
  

  Zach Scrivena : @silvia: Updated answer to include the inverse operation.

  paxdiablo : I have two questions: (1) When did Java introduce that for-statement syntax (it's nifty but my Eclipse flags error but it has 1.4)? (2) Why the hideous :-) bitshift, can't you just process two chars at a time?

  Zach Scrivena : @Pax: (1) for-each appeared in Java 1.5 http://java.sun.com/j2se/1.5.0/docs/guide/language/foreach.html (2) Doesn't seem to work unfortunately; Byte.parseByte("FF",16) throws a NumberFormatException.

  Zach Scrivena : @Pax: Integer.parseInt() works nicely of course =)

• Here's a complete program which includes the asBytes() function which is what I assume you were looking for, the opposite to asHex():

  public class Temp {
      public static String asHex (byte buf[]) {
          StringBuffer strbuf = new StringBuffer(buf.length * 2);
          int i;
          for (i = 0; i < buf.length; i++) {
              if (((int) buf[i] & 0xff) < 0x10)
                  strbuf.append("0");
              strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
          }
         return strbuf.toString();
      }
      public static byte[] asBytes (String s) {
          String s2;
          byte[] b = new byte[s.length() / 2];
          int i;
          for (i = 0; i < s.length() / 2; i++) {
              s2 = s.substring(i * 2, i * 2 + 2);
              b[i] = (byte)(Integer.parseInt(s2, 16) & 0xff);
          }
          return b;
      }
      static public void main(String args[]) {
          byte[] b = Temp.asBytes("010203040506070809fdfeff");
          String s = Temp.asHex(b);
          System.out.println (s);
      }
  }
  

• can anyone explain me the program which is written as

  public static String asHex (byte buf[]) { StringBuffer strbuf = new StringBuffer(buf.length * 2); int i;

  for (i = 0; i < buf.length; i++) {
      if (((int) buf[i] & 0xff) < 0x10)
          strbuf.append("0");
  
      strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
  }
  
  return strbuf.toString();
  

  }

• Check here for couple of good methods to do this.

• i need the explanation of the above code.urgent.please