java.util
Class UUID

java.lang.Object
  extended by java.util.UUID
All Implemented Interfaces:
Serializable, Comparable<UUID>

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

This class represents a 128-bit UUID value. There are several types of UUID, and while this class can be used to store them, only the Leach-Salz (variant 2) UUID specified in RFC-4122 will give meaningful results from the method calls. See: http://tools.ietf.org/html/4122 for the details The format of a Leach-Salz (variant 2) time-based (version 1) UUID is as follows: time_low - upper 32 bits of the most significant 64 bits, this is the least-significant part of the timestamp. time_mid - bits 16-31 of the most significant 64 bits, this is the middle portion of the timestamp. version - bits 8-15 of the most significant 64 bits. time_hi - bits 0-7 of the most significant 64 bits, the most significant portion of the timestamp. clock_and_reserved - bits 48-63 of the least significant 64 bits. a variable number of bits hold the variant (see the spec) node identifier - bits 0-47 of the least signficant 64 bits. These fields are valid only for version 1, in the remaining versions, only the version and variant fields are set, all others are used for data.

Since:
1.5
See Also:
Serialized Form

Constructor Summary
UUID(long mostSigBits, long leastSigBits)
          Constructs a new UUID.
 
Method Summary
 int clockSequence()
          Returns the clock-sequence value of this UUID.
 int compareTo(UUID o)
          Compare this UUID to another.
 boolean equals(Object obj)
          Compare a (UUID) object to this one
static UUID fromString(String name)
          Creates a UUID object from a Sting representation.
 long getLeastSignificantBits()
          Returns the least significant 64 bits of the UUID as a long.
 long getMostSignificantBits()
          Returns the most significant 64 bits of the UUID as a long.
 int hashCode()
          Returns a hash of this UUID.
static UUID nameUUIDFromBytes(byte[] name)
          Creates a UUID version 3 object (name based with MD5 hashing) from a series of bytes representing a name.
 long node()
          Returns the 48-bit node value in a long.
static UUID randomUUID()
          Generate a Leach-Salz (Variant 2) randomly generated (version 4) UUID.
 long timestamp()
          Returns the 60-bit timestamp value of the UUID in a long.
 String toString()
          Returns a String representation of the UUID.
 int variant()
          Returns the variant of the UUID This may be: 0 = Reserved for NCS backwards-compatibility 2 = Leach-Salz (supports the other methods in this class) 6 = Reserved for Microsoft backwards-compatibility 7 = (reserved for future use)
 int version()
          Returns the version # of the 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.

Since:
1.5
Method Detail

clockSequence

public int clockSequence()
Returns the clock-sequence value of this UUID. This field only exists in a time-based (version 1) UUID.

Throws:
UnsupportedOperationException - if the UUID type is not 1.

compareTo

public int compareTo(UUID o)
Compare this UUID to another. The comparison is performed as between two 128-bit integers.

Specified by:
compareTo in interface Comparable<UUID>
Parameters:
o - the object to be compared
Returns:
-1 if this < val, 0 if they are equal, 1 if this > val.

equals

public boolean equals(Object obj)
Compare a (UUID) object to this one

Overrides:
equals in class Object
Parameters:
obj - the Object to compare to
Returns:
whether this Object is semantically equal to another
See Also:
Object.hashCode()

fromString

public static UUID fromString(String name)
Creates a UUID object from a Sting representation. For the format of the string,

Returns:
a new UUID object.
See Also:
toString()

toString

public String toString()
Returns a String representation of the UUID. The format of the standard string representation (given in RFC4122) is: time-low "-" time-mid "-" time-high-and-version "-" clock-seq-and-reserved clock-seq-low "-" node Where each field is represented as a hex string.

Overrides:
toString in class Object
Returns:
the String representation.
See Also:
Object.getClass(), Object.hashCode(), Class.getName(), Integer.toHexString(int)

getLeastSignificantBits

public long getLeastSignificantBits()
Returns the least significant 64 bits of the UUID as a long.


getMostSignificantBits

public long getMostSignificantBits()
Returns the most significant 64 bits of the UUID as a long.


hashCode

public int hashCode()
Returns a hash of this UUID.

Overrides:
hashCode in class Object
Returns:
the hash code for this Object
See Also:
Object.equals(Object), System.identityHashCode(Object)

nameUUIDFromBytes

public static UUID nameUUIDFromBytes(byte[] name)
Creates a UUID version 3 object (name based with MD5 hashing) from a series of bytes representing a name.


node

public long node()
Returns the 48-bit node value in a long. This field only exists in a time-based (version 1) UUID.

Throws:
UnsupportedOperationException - if the UUID type is not 1.

timestamp

public long timestamp()
Returns the 60-bit timestamp value of the UUID in a long. This field only exists in a time-based (version 1) UUID.

Throws:
UnsupportedOperationException - if the UUID type is not 1.

randomUUID

public static UUID randomUUID()
Generate a Leach-Salz (Variant 2) randomly generated (version 4) UUID.


variant

public int variant()
Returns the variant of the UUID This may be: 0 = Reserved for NCS backwards-compatibility 2 = Leach-Salz (supports the other methods in this class) 6 = Reserved for Microsoft backwards-compatibility 7 = (reserved for future use)


version

public int version()
Returns the version # of the UUID. Valid version numbers for a variant 2 UUID are: 1 = Time based UUID 2 = DCE security UUID 3 = Name-based UUID using MD5 hashing 4 = Randomly generated UUID 5 = Name-based UUID using SHA-1 hashing

Returns:
the version number