The first and third method converted successfully with sign. The second one fail. The reason 3rd way working is : It convert to biginteger and convert to long (then we have sign),then convert back to biginteger (also with sign)
BigInteger i = BigInteger.valueOf(0xfffffffffffffff7l);
System.out.println(i);
System.out.println(i.toString(16));
System.out.println(String.valueOf(i.toString(16)));
BigInteger i2 = new BigInteger("1111111111111111111111111111111111111111111111111111111111110111", 2);
System.out.println(i2);
System.out.println(i2.toString(16));
System.out.println(String.valueOf(i2.toString(16)));
BigInteger i3 = BigInteger.valueOf(new BigInteger("1111111111111111111111111111111111111111111111111111111111110111", 2).longValue());
System.out.println(i3);
System.out.println(i3.toString(16));
System.out.println(String.valueOf(i3.toString(16)));
