Class UUID
- java.lang.Object
-
- java.util.UUID
- All Implemented Interfaces:
-
Serializable
,Comparable<UUID>
public final class UUID extends Object implements Serializable, Comparable<UUID>
A class that represents an immutable universally unique identifier (UUID). A UUID represents a 128-bit value.
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".
- Since:
- 1.5
- See Also:
- Serialized Form
Constructor Summary
Constructor | Description |
---|---|
UUID(long mostSigBits,
long leastSigBits) | Constructs a new |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
int | clockSequence() | The clock sequence value associated with this UUID. |
int | compareTo(UUID val) | Compares this UUID with the specified UUID. |
boolean | equals(Object obj) | Compares this object to the specified object. |
static UUID | fromString(String name) | Creates a |
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 |
static UUID | nameUUIDFromBytes(byte[] name) | Static factory to retrieve a type 3 (name based) |
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 |
int | variant() | The variant number associated with this |
int | version() | The version number associated with this |
Methods declared in class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Constructor Detail
UUID
public UUID(long mostSigBits, long leastSigBits)
Constructs a new 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
.
- Parameters:
-
mostSigBits
- The most significant bits of theUUID
-
leastSigBits
- The least significant bits of theUUID
Method Detail
randomUUID
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
nameUUIDFromBytes
public static UUID nameUUIDFromBytes(byte[] name)
Static factory to retrieve a type 3 (name based) UUID
based on the specified byte array.
- Parameters:
-
name
- A byte array to be used to construct aUUID
- Returns:
- A
UUID
generated from the specified array
fromString
public static UUID fromString(String name)
Creates a UUID
from the string standard representation as described in the toString()
method.
- Parameters:
-
name
- A string that specifies aUUID
- Returns:
- A
UUID
with the specified value - Throws:
-
IllegalArgumentException
- If name does not conform to the string representation as described intoString()
getLeastSignificantBits
public long getLeastSignificantBits()
Returns the least significant 64 bits of this UUID's 128 bit value.
- Returns:
- The least significant 64 bits of this UUID's 128 bit value
getMostSignificantBits
public long getMostSignificantBits()
Returns the most significant 64 bits of this UUID's 128 bit value.
- Returns:
- The most significant 64 bits of this UUID's 128 bit value
version
public int version()
The version number associated with this UUID
. The version number describes how this UUID
was generated. The version number has the following meaning:
- 1 Time-based UUID
- 2 DCE security UUID
- 3 Name-based UUID
- 4 Randomly generated UUID
- Returns:
- The version number of this
UUID
variant
public int variant()
The variant number associated with this UUID
. The variant number describes the layout of the UUID
. The variant number has the following meaning:
- 0 Reserved for NCS backward compatibility
- 2 IETF RFC 4122 (Leach-Salz), used by this class
- 6 Reserved, Microsoft Corporation backward compatibility
- 7 Reserved for future definition
- Returns:
- The variant number of this
UUID
timestamp
public long timestamp()
The timestamp value associated with this UUID.
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.
- Returns:
- The timestamp of this
UUID
. - Throws:
-
UnsupportedOperationException
- If this UUID is not a version 1 UUID
clockSequence
public int clockSequence()
The clock sequence value associated with this UUID.
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.
- Returns:
- The clock sequence of this
UUID
- Throws:
-
UnsupportedOperationException
- If this UUID is not a version 1 UUID
node
public long node()
The node value associated with this UUID.
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.
- Returns:
- The node value of this
UUID
- Throws:
-
UnsupportedOperationException
- If this UUID is not a version 1 UUID
toString
public String toString()
Returns a 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"
hashCode
public int hashCode()
Returns a hash code for this UUID
.
- Overrides:
-
hashCode
in classObject
- Returns:
- A hash code value for this
UUID
- See Also:
-
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)
equals
public boolean equals(Object obj)
Compares this object to the specified object. The result is
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
.
- Overrides:
-
equals
in classObject
- Parameters:
-
obj
- The object to be compared - Returns:
-
true
if the objects are the same;false
otherwise - See Also:
-
Object.hashCode()
,HashMap
compareTo
public int compareTo(UUID val)
Compares this UUID with the specified UUID.
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.
- Specified by:
-
compareTo
in interfaceComparable<UUID>
- Parameters:
-
val
-UUID
to which thisUUID
is to be compared - Returns:
- -1, 0 or 1 as this
UUID
is less than, equal to, or greater thanval