java.util.UUID

public final class java.util

UUID

Java SE 6

Implements: Serializable, Comparable

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 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 UUIDs, see RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace, section 4.2 "Algorithms for Creating a Time-Based UUID".

version 1.18, 06/02/06

since 1.5

Constructors

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.

mostSigBits
leastSigBits

Methods

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.

return the clock sequence of this UUID.

Throws UnsupportedOperationException: if this UUID is not a version 1 UUID.

public int

compareTo(UUID val)
Compares this UUID with the specified UUID.

The first of two UUIDs follows the second if the most significant field in which the UUIDs differ is greater for the first UUID.

val UUID to which this UUID is to be compared.

return -1, 0 or 1 as this UUID is less than, equal to, or greater than val.

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.

obj	the object to compare with.
return	`true` if the objects are the same; `false` otherwise.

public static UUID

fromString(String name)
Creates a UUID from the string standard representation as described in the #toString method.

name	a string that specifies a `UUID`.
return	a `UUID` with the specified value.
Throws	IllegalArgumentException: if name does not conform to the string representation as described in `#toString`.

public int

hashCode()
Returns a hash code for this UUID.

return a hash code value for this UUID.

public static UUID

nameUUIDFromBytes(byte[] name)
Static factory to retrieve a type 3 (name based) UUID based on the specified byte array.

name	a byte array to be used to construct a `UUID`.
return	a `UUID` generated from the specified array.

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.

return the node value of this UUID.

Throws UnsupportedOperationException: if this UUID is not a version 1 UUID.

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.

return a randomly generated UUID.

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.

Throws UnsupportedOperationException: if this UUID is not a version 1 UUID.

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"

return a string representation of this UUID.

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 The Leach-Salz variant (used by this class)
6 Reserved, Microsoft Corporation backward compatibility
7 Reserved for future definition

return the variant number of this UUID.

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

return the version number of this UUID.

Properties

public long

getLeastSignificantBits()
Returns the least significant 64 bits of this UUID's 128 bit value.

return

the least significant 64 bits of this UUID's 128 bit value.

public long

getMostSignificantBits()
Returns the most significant 64 bits of this UUID's 128 bit value.

return

the most significant 64 bits of this UUID's 128 bit value.

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