Home » openjdk-7 » java » util » [javadoc | source]
java.util
public final class: UUID [javadoc | source]
java.lang.Object
   java.util.UUID

All Implemented Interfaces:
    Comparable, java$io$Serializable

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 {@code UUID}. The bit layout described above is valid only for a {@code 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 {@code 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 {@code UUID}s, see RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace, section 4.2 "Algorithms for Creating a Time-Based UUID".

Constructor:
 public UUID(long mostSigBits,
    long leastSigBits) 
Method from java.util.UUID Summary:
clockSequence,   compareTo,   equals,   fromString,   getLeastSignificantBits,   getMostSignificantBits,   hashCode,   nameUUIDFromBytes,   node,   randomUUID,   timestamp,   toString,   variant,   version
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.util.UUID Detail:
 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 {@code 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.

 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.

 public boolean equals(Object obj) 
    Compares this object to the specified object. The result is {@code true} if and only if the argument is not {@code null}, is a {@code UUID} object, has the same variant, and contains the same value, bit for bit, as this {@code UUID}.
 public static UUID fromString(String name) 
    Creates a {@code UUID} from the string standard representation as described in the #toString method.
 public long getLeastSignificantBits() 
    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.
 public int hashCode() 
    Returns a hash code for this {@code UUID}.
 public static UUID nameUUIDFromBytes(byte[] name) 
    Static factory to retrieve a type 3 (name based) {@code UUID} based on the specified byte 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.

 public static UUID randomUUID() 
    Static factory to retrieve a type 4 (pseudo randomly generated) UUID. The {@code UUID} is generated using a cryptographically strong pseudo random number generator.
 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 {@code 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 {@code UUID} is not a time-based UUID then this method throws UnsupportedOperationException.

 public String toString() 
    Returns a {@code String} object representing this {@code UUID}.

    The UUID string representation is as described by this BNF:

    {@code
    UUID                   =  "-"  "-"
                              "-"
                              "-"
                             
    time_low               = 4*
    time_mid               = 2*
    time_high_and_version  = 2*
    variant_and_sequence   = 2*
    node                   = 6*
    hexOctet               = 
    hexDigit               =
          "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
          | "a" | "b" | "c" | "d" | "e" | "f"
          | "A" | "B" | "C" | "D" | "E" | "F"
    }
 public int variant() 
    The variant number associated with this {@code UUID}. The variant number describes the layout of the {@code 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
 public int version() 
    The version number associated with this {@code UUID}. The version number describes how this {@code 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