Java：有符号长字符串到无符号长字符串

有没有一种简单快速的方法将 Java 有符号长字符串转换为无符号长字符串？

-1                    ->  "18446744073709551615"
-9223372036854775808  ->  "09223372036854775808"
 9223372036854775807  ->  "09223372036854775807"
 0                    ->  "00000000000000000000"

这是使用 BigInteger 的解决方案：

/** the constant 2^64 */
private static final BigInteger TWO_64 = BigInteger.ONE.shiftLeft(64);

public String asUnsignedDecimalString(long l) {
   BigInteger b = BigInteger.valueOf(l);
   if(b.signum() < 0) {
      b = b.add(TWO_64);
   }
   return b.toString();
}

This works since the unsigned value of a (signed) number in two-s complement is just 2^{(number of bits)} more than the signed value, and Java's long has 64 bits.

BigInteger 有这个很好的toString()我们可以在这里使用的方法。