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 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".

Public Constructor Summary

UUID(long mostSigBits, long leastSigBits)

Constructs a new UUID using the specified data.

Public Method Summary

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 `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(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 a `String` object representing this `UUID`.
int	variant() The variant number associated with this `UUID`.
int	version() The version number associated with this `UUID`.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this `Object`.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of `Class` that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object.

From interface java.lang.Comparable

abstract int

compareTo(UUID o)

Compares this object with the specified object for order.

Public 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.

Parameters

mostSigBits	The most significant bits of the `UUID`
leastSigBits	The least significant bits of the `UUID`

Public 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.

Returns

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 is greater than the second if the most significant field in which the UUIDs differ is greater for the first UUID.

Parameters

val	`UUID` to which this `UUID` is to be compared

Returns

-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.

Parameters

obj	The object to be compared

Returns

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.

Parameters

name	A string that specifies a `UUID`

Returns

A UUID with the specified value

Throws

IllegalArgumentException	If name does not conform to the string representation as described in `toString()`

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

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

public int hashCode ()

Returns a hash code for this UUID.

Returns

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.

Parameters

name	A byte array to be used to construct a `UUID`

Returns

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.

Returns

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.

Returns

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.

Returns

The timestamp of this UUID.

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"

Returns

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 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

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