CharBuffer.toString() trap-Example: int32toHex

使用CharBuffer.toString()時, 要注意, 輸出的字串, 是從指標所在的位置開始寫的, 因此, 在輸出之前, 要加上: position(0), 如:
以下是一個範例, 將32位元有正負的整數, 傳成十六進位數字,
 /**
  * Convert 32 bits integer number to hex-decimal string
  * @param num number to convert
  * @return hex-decimal string
  */
public static String Int32ToHex(int num) {
  final int BUFFER_SIZE=8;
  final int BITS=32;
  String pattern="0123456789ABCDEF";
  CharBuffer digits=CharBuffer.allocate(BUFFER_SIZE);
  int digit=0;
  int ref=0x80000000;
  int bitValue=0x8;
  for(int i=0;i<BITS;++i) {
      int offset=i%4;
      if(offset==0 && i!=0) {
      digits.append(pattern.charAt(digit));
      digit=0;
      bitValue=0x8;
   }
   if((num & ref)!=0) digit += bitValue;
   bitValue >>= 1;
   /***
    * Notice that,
    *        0x80000000(-2147483648) >> 1 is NOT 0x40000000, but 0xC0000000(-1073741824)
    *        (-->E0000000(536870912)-->F0000000(268435456)-->F8000000(-134217728))
    *        Always divide by 2, no matter positive or negative number
    * and 0xFFFFFFFF(-1) >> 1 is NOT 0x7FFFFFFF, but still 0xFFFFFFFF
    * For the positive integer, the bit operation is running just as expectation.
    */   if(ref==0x80000000) ref=0x40000000;
   else ref >>= 1;
  }
  digits.append(pattern.charAt(digit));
  digits.position(0);
  return digits.toString();
}