UUID (Java Platform SE 7 )

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 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".
Since:

1.5

See Also:
Serialized Form

Constructor Summary

Constructors
Constructor and Description

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

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

Method Summary

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 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`.

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - 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 Detail
  - 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
  - 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
    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 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.
    
    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:
    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 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:
    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 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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Class UUID

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

UUID

Method Detail

randomUUID

nameUUIDFromBytes

fromString

getLeastSignificantBits

getMostSignificantBits

version

variant

timestamp

clockSequence

node

toString

hashCode

equals

compareTo