Added in API level 1

Summary: Ctors | Methods | Inherited Methods

UUID

public final class UUID
extends Object implements Comparable<UUID>, Serializable

java.lang.Object
↳	java.util.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".

Summary

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

Public methods
`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 methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the 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.
`String`	`toString()` Returns a string representation of the object.
`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.
`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()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

From interface


        
          java.lang.Comparable


      compareTo(UUID o)

Compares this object with the specified object for order.

Public constructors

UUID

Added in API level 1

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`	`long`: The most significant bits of the `UUID`
`leastSigBits`	`long`: The least significant bits of the `UUID`

Public methods

clockSequence

Added in API level 1

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
`int`	The clock sequence of this `UUID`

Throws
`UnsupportedOperationException`	If this UUID is not a version 1 UUID

compareTo

Added in API level 1

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

Returns
`int`	-1, 0 or 1 as this `UUID` is less than, equal to, or greater than `val`

equals

Added in API level 1

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`	`Object`: The object to be compared

Returns
`boolean`	`true` if the objects are the same; `false` otherwise

fromString

Added in API level 1

public static UUID fromString (String name)

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

Parameters
`name`	`String`: A string that specifies a `UUID`

Returns
`UUID`	A `UUID` with the specified value

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

getLeastSignificantBits

Added in API level 1

public long getLeastSignificantBits ()

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

Returns
`long`	The least significant 64 bits of this UUID's 128 bit value

getMostSignificantBits

Added in API level 1

public long getMostSignificantBits ()

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

Returns
`long`	The most significant 64 bits of this UUID's 128 bit value

hashCode

Added in API level 1

public int hashCode ()

Returns a hash code for this UUID.

Returns
`int`	A hash code value for this `UUID`

nameUUIDFromBytes

Added in API level 1

public static UUID nameUUIDFromBytes (byte[] name)

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

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

Returns
`UUID`	A `UUID` generated from the specified array

node

Added in API level 1

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
`long`	The node value of this `UUID`

Throws
`UnsupportedOperationException`	If this UUID is not a version 1 UUID

randomUUID

Added in API level 1

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
`UUID`	A randomly generated `UUID`

timestamp

Added in API level 1

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
`long`	The timestamp of this `UUID`.

Throws
`UnsupportedOperationException`	If this UUID is not a version 1 UUID

toString

Added in API level 1

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
`String`	A string representation of this `UUID`

variant

Added in API level 1

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
`int`	The variant number of this `UUID`

version

Added in API level 1

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
`int`	The version number of this `UUID`