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_hi
The 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 aUUID
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
Constructors Constructor and Description UUID(long mostSigBits, long leastSigBits)
Constructs a newUUID
using the specified data.
-
Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method and 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 aUUID
from the string standard representation as described in thetoString()
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 thisUUID
.static UUID
nameUUIDFromBytes(byte[] name)
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 aString
object representing thisUUID
.int
variant()
The variant number associated with thisUUID
.int
version()
The version number associated with thisUUID
.
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Constructor Detail
UUID
public UUID(long mostSigBits, long leastSigBits)
Constructs a newUUID
using the specified data.mostSigBits
is used for the most significant 64 bits of theUUID
andleastSigBits
becomes the least significant 64 bits of theUUID
.- 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. TheUUID
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 aUUID
from the string standard representation as described in thetoString()
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 thisUUID
. The version number describes how thisUUID
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 thisUUID
. The variant number describes the layout of theUUID
. 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 aString
object representing thisUUID
.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 thisUUID
.- 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 istrue
if and only if the argument is notnull
, is aUUID
object, has the same variant, and contains the same value, bit for bit, as thisUUID
.- 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
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