Serializable
, Comparable<UUID>
public final class UUID extends Object implements Serializable, Comparable<UUID>
There exist different variants of these global identifiers. The methods of this class are for manipulating the Leach-Salz variant, although the constructors allow the creation of any variant of UUID (described below).
The layout of a variant 2 (Leach-Salz) UUID is as follows: The most significant long consists of the following unsigned fields:
0xFFFFFFFF00000000 time_low 0x00000000FFFF0000 time_mid 0x000000000000F000 version 0x0000000000000FFF time_hiThe least significant long consists of the following unsigned fields:
0xC000000000000000 variant 0x3FFF000000000000 clock_seq 0x0000FFFFFFFFFFFF node
The variant field contains a value which identifies the layout of the UUID
. The bit layout described above is valid only for a
UUID
with a variant value of 2, which indicates the Leach-Salz variant.
The version field holds a value that describes the type of this
UUID
. There are four different basic types of UUIDs: time-based, DCE security, name-based, and randomly generated UUIDs. These types have a version value of 1, 2, 3 and 4, respectively.
For more information including algorithms used to create UUID
s, see RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace, section 4.2 "Algorithms for Creating a Time-Based UUID".
Constructor | Description |
---|---|
UUID |
Constructs a new UUID using the specified data. |
Modifier and Type | Method | Description |
---|---|---|
int |
clockSequence() |
The clock sequence value associated with this UUID. |
int |
compareTo |
Compares this UUID with the specified UUID. |
boolean |
equals |
Compares this object to the specified object. |
static UUID |
fromString |
Creates a UUID from the string standard representation as described in the toString() method. |
long |
getLeastSignificantBits() |
Returns the least significant 64 bits of this UUID's 128 bit value. |
long |
getMostSignificantBits() |
Returns the most significant 64 bits of this UUID's 128 bit value. |
int |
hashCode() |
Returns a hash code for this UUID . |
static UUID |
nameUUIDFromBytes |
Static factory to retrieve a type 3 (name based) UUID based on the specified byte array. |
long |
node() |
The node value associated with this UUID. |
static UUID |
randomUUID() |
Static factory to retrieve a type 4 (pseudo randomly generated) UUID. |
long |
timestamp() |
The timestamp value associated with this UUID. |
String |
toString() |
Returns a String object representing this UUID . |
int |
variant() |
The variant number associated with this UUID . |
int |
version() |
The version number associated with this UUID . |
public UUID(long mostSigBits, long leastSigBits)
UUID
using the specified data.
mostSigBits
is used for the most significant 64 bits of the
UUID
and leastSigBits
becomes the least significant 64 bits of the UUID
.mostSigBits
- The most significant bits of the UUID
leastSigBits
- The least significant bits of the UUID
public static UUID randomUUID()
UUID
is generated using a cryptographically strong pseudo random number generator.UUID
public static UUID nameUUIDFromBytes(byte[] name)
UUID
based on the specified byte array.name
- A byte array to be used to construct a UUID
UUID
generated from the specified arraypublic static UUID fromString(String name)
UUID
from the string standard representation as described in the toString()
method.name
- A string that specifies a UUID
UUID
with the specified valueIllegalArgumentException
- If name does not conform to the string representation as described in toString()
public long getLeastSignificantBits()
public long getMostSignificantBits()
public int version()
UUID
. The version number describes how this UUID
was generated. The version number has the following meaning: UUID
public int variant()
UUID
. The variant number describes the layout of the UUID
. The variant number has the following meaning: UUID
public long timestamp()
The 60 bit timestamp value is constructed from the time_low, time_mid, and time_hi fields of this UUID
. The resulting timestamp is measured in 100-nanosecond units since midnight, October 15, 1582 UTC.
The timestamp value is only meaningful in a time-based UUID, which has version type 1. If this UUID
is not a time-based UUID then this method throws UnsupportedOperationException.
UUID
.UnsupportedOperationException
- If this UUID is not a version 1 UUIDpublic int clockSequence()
The 14 bit clock sequence value is constructed from the clock sequence field of this UUID. The clock sequence field is used to guarantee temporal uniqueness in a time-based UUID.
The clockSequence
value is only meaningful in a time-based UUID, which has version type 1. If this UUID is not a time-based UUID then this method throws UnsupportedOperationException.
UUID
UnsupportedOperationException
- If this UUID is not a version 1 UUIDpublic long node()
The 48 bit node value is constructed from the node field of this UUID. This field is intended to hold the IEEE 802 address of the machine that generated this UUID to guarantee spatial uniqueness.
The node value is only meaningful in a time-based UUID, which has version type 1. If this UUID is not a time-based UUID then this method throws UnsupportedOperationException.
UUID
UnsupportedOperationException
- If this UUID is not a version 1 UUIDpublic String toString()
String
object representing this UUID
. 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"
public int hashCode()
UUID
.public boolean equals(Object obj)
true
if and only if the argument is not null
, is a UUID
object, has the same variant, and contains the same value, bit for bit, as this UUID
.public int compareTo(UUID val)
The first of two UUIDs is greater than the second if the most significant field in which the UUIDs differ is greater for the first UUID.
compareTo
in interface Comparable<UUID>
val
- UUID
to which this UUID
is to be comparedUUID
is less than, equal to, or greater than val
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Documentation extracted from Debian's OpenJDK Development Kit package.
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