Package net.jini.id

Class Uuid

java.lang.Object
net.jini.id.Uuid
All Implemented Interfaces:
Serializable
public class Uuid extends Object implements Serializable
A 128-bit value to serve as a universally unique identifier. Two Uuids are equal if they have the same 128-bit value. Uuid instances can be created using the static methods of the UuidFactory class.

The design of this class is intended to support the use of universally unique identifiers that

  1. have a high likelihood of uniqueness over space and time and
  2. are computationally difficult to guess.
The second goal is intended to support the treatment of data containing a Uuid as a capability. Note that not all defined Uuid values imply a generation algorithm that supports this goal.

The most significant 64 bits of the value can be decomposed into unsigned integer fields according to the following bit masks: 

 0xFFFFFFFF00000000     time_low
 0x00000000FFFF0000     time_mid
 0x000000000000F000     version
 0x0000000000000FFF     time_hi

The least significant 64 bits of the value can be decomposed into unsigned integer fields according to the following bit masks: 

 0xC000000000000000     variant
 0x3FFF000000000000     clock_seq
 0x0000FFFFFFFFFFFF     node

This specification defines the meaning (and implies aspects of the generation algorithm) of Uuid values if the variant field is 0x2 and the version field is either 0x1 or 0x4.

If the version field is 0x1, then

  • the time_low, time_mid, and time_hi fields are the least, middle, and most significant bits (respectively) of a 60-bit timestamp of 100-nanosecond intervals since midnight, October 15, 1582 UTC,
  • the clock_seq field is a 14-bit number chosen to help avoid duplicate Uuid values in the event of a changed node address or a backward system clock adjustment (such as a random number when in doubt, or the previously used number incremented by one if just a backward clock adjustment is detected), and
  • the node field is an IEEE 802 address (a 48-bit value).

    As an alternative to an IEEE 802 address (such as if one is not available to the generation algorithm), the node field may also be a 48-bit number for which the most significant bit is set to 1 and the remaining bits were produced from a cryptographically strong random sequence.

If the version field is 0x4, then the time_low, time_mid, time_hi, clock_seq, and node fields are values that were produced from a cryptographically strong random sequence.

Only Uuid values with a version field of 0x4 are considered computationally difficult to guess. A Uuid value with a version field of 0x1 should not be treated as a capability.

A subclass of Uuid must not implement Externalizable; this restriction is enforced by this class's constructor and readObject methods.

Since:
2.0
Author:
Sun Microsystems, Inc.
See Also:

  • Constructor Summary

    Constructors
    Constructor
    Description
    Uuid(long bits0, long bits1)
    Creates a new Uuid with the specified 128-bit value.

  • Method Summary

    Modifier and Type
    Method
    Description
    final boolean
    equals(Object obj)
    Compares the specified object with this Uuid for equality.
    protected final void
    finalize()
    Delegates to the superclass's finalize method.
    final long
    getLeastSignificantBits()
    Returns the least significant 64 bits of this Uuid's 128-bit value.
    final long
    getMostSignificantBits()
    Returns the most significant 64 bits of this Uuid's 128-bit value.
    final int
    hashCode()
    Returns the hash code value for this Uuid.
    protected final Object
    readResolve()
    Returns this object.
    final String
    toString()
    Returns a string representation of this Uuid.
    final void
    write(OutputStream out)
    Marshals a binary representation of this Uuid to an OutputStream.
    protected final Object
    writeReplace()
    Returns this object.

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • Uuid

      public Uuid(long bits0, long bits1)
      Creates a new Uuid with the specified 128-bit value.
      Parameters:
      bits0 - the most significant 64 bits of the 128-bit value
      bits1 - the least significant 64 bits of the 128-bit value
      Throws:
      SecurityException - if the class of this object implements Externalizable

  • Method Details

    • getMostSignificantBits

      public final long getMostSignificantBits()
      Returns the most significant 64 bits of this Uuid's 128-bit value.
      Returns:
      the most significant 64 bits of the 128-bit value

    • getLeastSignificantBits

      public final long getLeastSignificantBits()
      Returns the least significant 64 bits of this Uuid's 128-bit value.
      Returns:
      the least significant 64 bits of the 128-bit value

    • hashCode

      public final int hashCode()
      Returns the hash code value for this Uuid.
      Overrides:
      hashCode in class Object
      Returns:
      the hash code value for this Uuid

    • equals

      public final boolean equals(Object obj)
      Compares the specified object with this Uuid for equality. This method returns true if and only if the specified object is a Uuid instance with the same 128-bit value as this one.
      Overrides:
      equals in class Object
      Parameters:
      obj - the object to compare this Uuid to
      Returns:
      true if the given object is equivalent to this one, and false otherwise

    • toString

      public final String toString()
      Returns a string representation of this Uuid.

      The string representation is 36 characters long, with five fields of zero-filled, lowercase hexadecimal numbers separated by hyphens. The fields of the string representation are derived from the components of the 128-bit value in the following order:

      • time_low (8 hexadecimal digits)
      • time_mid (4 hexadecimal digits)
      • version and time_hi treated as a single field (4 hexadecimal digits)
      • variant and clock_seq treated as a single field (4 hexadecimal digits)
      • node (12 hexadecimal digits)

      As an example, a Uuid with the 128-bit value 

      0x0123456789ABCDEF0123456789ABCDEF
      would have the following string representation: 
      01234567-89ab-cdef-0123-456789abcdef
      Overrides:
      toString in class Object
      Returns:
      a string representation of this Uuid

    • write

      public final void write(OutputStream out) throws IOException
      Marshals a binary representation of this Uuid to an OutputStream.

      Specifically, this method writes the 128-bit value to the stream as 16 bytes in network (big-endian) byte order.

      Parameters:
      out - the OutputStream to write this Uuid to
      Throws:
      IOException - if an I/O exception occurs while performing this operation
      NullPointerException - if out is null

    • finalize

      protected final void finalize() throws Throwable
      Delegates to the superclass's finalize method. This method prevents a subclass from declaring an overriding finalize method.
      Overrides:
      finalize in class Object
      Throws:
      Throwable - if the superclass's finalize method throws a Throwable

    • writeReplace

      protected final Object writeReplace()
      Returns this object. This method prevents a subclass from declaring a writeReplace method with an alternate implementation.
      Returns:
      this object

    • readResolve

      protected final Object readResolve()
      Returns this object. This method prevents a subclass from declaring a readResolve method with an alternate implementation.
      Returns:
      this object