java.util.UUID.randomUUID().toString() length

user_7909529 0
Viewed 68150

Does java.util.UUID.randomUUID().toString() length always equal to 36?

I was not able to find info on that. Here it is said only the following:

public static UUID randomUUID() Static factory to retrieve a type 4 (pseudo randomly generated) UUID. The UUID is generated using a cryptographically strong pseudo random number generator. Returns: A randomly generated UUID

And that type 4 tells me nothing. I do not know what type 4 means in the case.

string-length uuid random java string
3 Answers

You may convert UUIDv4 16 bytes binary to 24 bytes ascii using base64, instead encode to ascii-hex (32 bytes)

user_92665900

For those like me that start googling before reading the javadoc, here the javadoc ;)

UUID.toString

For those that Don't know how to read a grammar tree read from Bottom to Top.
an hexDigit is one char
an hexOctet is 2 hexDigits = 2chars
a node is 6 * hexOctet = 6 * 2hexdigit = 6*2 chars = 12chars
a variant_and_sequence is 2 * hexOctet = 2 * 2hexdigit = 2*2 chars = 4chars
a time_high_and_version is 2 * hexOctet = 2 * 2hexdigit = 2*2 chars = 4chars
a time_mid is 2 * hexOctet = 2 * 2hexdigit = 2*2 chars = 4chars
a time_low is 4 * hexOctet = 4* 2hexdigit = 4*2 chars = 8chars
and finaly, a UUID is < time_low > "-" < time_mid > "-" < time_high_and_version > "-" < variant_and_sequence > "-"< node >

= 8 chars + 1 char + 4 chars + 1 char + 4 chars + 1 char + 4 chars + 1 char + 12 chars

= 36 chars ! 128 bit of data + 4 hyphen as stated previously

The UUID string representation is as described by this BNF: 

 UUID                   = <time_low> "-" <time_mid> "-"
                          <time_high_and_version> "-"
                          <variant_and_sequence> "-"
                          <node>
 time_low               = 4*<hexOctet>
 time_mid               = 2*<hexOctet>
 time_high_and_version  = 2*<hexOctet>
 variant_and_sequence   = 2*<hexOctet>
 node                   = 6*<hexOctet>
 hexOctet               = <hexDigit><hexDigit>
 hexDigit               =
       "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
       | "a" | "b" | "c" | "d" | "e" | "f"
       | "A" | "B" | "C" | "D" | "E" | "F"
user_35013450
Related