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.

This class is primarily designed for manipulating Leach-Salz variant UUIDs, but it also supports the creation of UUIDs of other variants.

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.

See RFC 9562: Universally Unique Identifiers (UUIDs) for the complete specification, including the UUID format, layouts, and algorithms for creating UUIDs.

There are eight defined types of UUIDs, each identified by a version number: time-based (version 1), DCE security (version 2), name-based with MD5 (version 3), randomly generated (version 4), name-based with SHA-1 (version 5), reordered time-based (version 6), Unix epoch time-based (version 7), and custom-defined layout (version 8).

Since:

1.5

External Specifications

See Also:

Constructor Summary

Constructor	Description
`UUID(long mostSigBits, long leastSigBits)`	Constructs a new `UUID` using the specified data.

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 `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`	`ofEpochMillis(long timestamp)`	Creates a type 7 UUID (UUIDv7) `UUID` from the given Unix Epoch timestamp.
`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`.

Methods declared in class Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Modifier and Type	Method	Description
`protected Object`	`clone()`	Creates and returns a copy of this object.
`protected void`	`finalize()`	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
`final Class<?>`	`getClass()`	Returns the runtime class of this `Object`.
`final void`	`notify()`	Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()`	Wakes up all threads that are waiting on this object's monitor.
`final void`	`wait()`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`	`wait(long timeoutMillis)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis, int nanos)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

Constructor Details

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 the UUID; leastSigBits - The least significant bits of the UUID

Method Details

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 a UUID
Returns:: A UUID generated from the specified array

ofEpochMillis

public static UUID ofEpochMillis(long timestamp)

Creates a type 7 UUID (UUIDv7) UUID from the given Unix Epoch timestamp. The returned UUID will have the given timestamp in the first 6 bytes, followed by the version and variant bits representing UUIDv7, and the remaining bytes will contain random data from a cryptographically strong pseudo-random number generator.

API Note:: UUIDv7 values are created by allocating a Unix timestamp in milliseconds in the most significant 48 bits, allocating the required version (4 bits) and variant (2-bits) and filling the remaining 74 bits with random bits. As such, this method rejects timestamp values that do not fit into 48 bits.
Monotonicity (each subsequent value being greater than the last) is a primary characteristic of UUIDv7 values. This is due to the timestamp value being part of the UUID. Callers of this method that wish to generate monotonic UUIDv7 values are expected to ensure that the given timestamp value is monotonic.
Parameters:: timestamp - the number of milliseconds since midnight 1 Jan 1970 UTC, leap seconds excluded.
Returns:: a UUID constructed using the given timestamp
Throws:: IllegalArgumentException - if the timestamp is negative or greater than (1L << 48) - 1
Since:: 26

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 a UUID
Returns:: A UUID with the specified value
Throws:: IllegalArgumentException - If name does not conform to the string representation as described in toString()

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
7 Unix Epoch time-based 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 9562 (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"

Overrides:: toString in class Object
Returns:: A string representation of this UUID

hashCode

public int hashCode()

Returns a hash code for this UUID.

Overrides:

hashCode in class Object

Returns:

A hash code value for this UUID

See Also:

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 class Object

Parameters:

obj - The object to be compared

Returns:

true if the objects are the same; false otherwise

See Also:

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 interface Comparable<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

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