There are many ways, e.g. by using a regexp, by using a loop and indeed
comparing characters for being within 0-9, a-f, A-F, by comparing
against Character.digit(char, 16) in a loop, etc.

/Thomas

Maybe something like this:

public boolean isHexDigit(String hexDigit)
{
    char[] hexDigitArray = hexDigit.toCharArray();
    int hexDigitLength = hexDigitArray.length;

    boolean isNotHex;
    for (int i = 0; i < hexDigitLength; i++) {
        isNotHex = Character.digit(hexDigitArray[i], 16) == -1;
        if (isNotHex) {
            return false;
        }
    }

    return true;
}

There are many ways as people have talked about.  looping through all
digits and checking for the ranges.  But probably the easiet thing to
do is follow your instinct.

boolean isHex(String str)
{
  int test = 0;
  try
  {
    test = Integer.parseInt(str);
  }
  catch(Exception e)
  {
     return false;
  }
  return true;
}

This should be fine unless your really in tight processing loop, then
you may not want to be doing the check via exceptions.  I was almost
sure the Character class had something like this...but it seems like it
can only tell if its a decimal digit.

On the other hand, depending on the larger context on where this will
be used, u might not want to do the explicit check and just rely on
exception handling itself.

Yamin Bismilla

There are many ways as people have talked about.  looping through all
digits and checking for the ranges.  But probably the easiet thing to
do is follow your instinct.

boolean isHex(String str)
{
  int test = 0;
  try
  {
    test = Integer.parseInt(str);
  }
  catch(Exception e)
  {
     return false;
  }
  return true;
}

This should be fine unless your really in tight processing loop, then
you may not want to be doing the check via exceptions.  I was almost
sure the Character class had something like this...but it seems like it
can only tell if its a decimal digit.

On the other hand, depending on the larger context on where this will
be used, u might not want to do the explicit check and just rely on
exception handling itself.

Yamin Bismilla

Should "-f" be accepted or rejected?

If you literally want all hex digits, it should be rejected, and you
should use a looping character check. If you want a string that
represents an integer in hex, it should be accepted.

Integer.parseInt("-f",16) returns -15 with no exception.

Patricia

String.matches("\\p{XDigit}+");

this is close, Return a boolean instead of an int.

/**
* convert a single char to corresponding nibble.
*
* @param c char to convert. must be 0-9 a-f A-F, no
* spaces, plus or minus signs.
*
* @return corresponding integer
*/
private static int charToNibble ( char c )
  {
  if ( '0' <= c && c <= '9' )
     {
     return c - '0';
     }
  else if ( 'a' <= c && c <= 'f' )
     {
     return c - 'a' + 0xa;
     }
  else if ( 'A' <= c && c <= 'F' )
     {
     return c - 'A' + 0xa;
     }
  else
     {
     throw new IllegalArgumentException ( "Invalid hex character: " +
c );
     }
  }

See http://mindprod.com/jgloss/hex.html