Package java.util

Class UUID

java.lang.Object
java.util.UUID
All Implemented Interfaces:
Serializable, Comparable<UUID>
public final class UUID
extends Object
implements Serializable, Comparable<UUID>
UUID is an immutable representation of a 128-bit universally unique identifier (UUID).

There are multiple, variant layouts of UUIDs, but this class is based upon variant 2 of RFC 4122, the Leach-Salz variant. This class can be used to model alternate variants, but most of the methods will be unsupported in those cases; see each method for details.

Since:
1.5
See Also:
Serialized Form

  • Constructor Details

    • UUID

      public UUID​(long mostSigBits, long leastSigBits)

      Constructs an instance with the specified bits.

      Parameters:
      mostSigBits - The 64 most significant bits of the UUID.
      leastSigBits - The 64 least significant bits of the UUID.

  • Method Details

    • randomUUID

      public static UUID randomUUID()

      Generates a variant 2, version 4 (randomly generated number) UUID as per RFC 4122.

      Returns:
      an UUID instance.

    • nameUUIDFromBytes

      public static UUID nameUUIDFromBytes​(byte[] name)

      Generates a variant 2, version 3 (name-based, MD5-hashed) UUID as per RFC 4122.

      Parameters:
      name - the name used as byte array to create an UUID.
      Returns:
      an UUID instance.

    • fromString

      public static UUID fromString​(String uuid)

      Parses a UUID string with the format defined by toString().

      Parameters:
      uuid - the UUID string to parse.
      Returns:
      an UUID instance.
      Throws:
      NullPointerException - if uuid is null.
      IllegalArgumentException - if uuid is not formatted correctly.

    • getLeastSignificantBits

      public long getLeastSignificantBits()

      The 64 least significant bits of the UUID.

      Returns:
      the 64 least significant bits.

    • getMostSignificantBits

      public long getMostSignificantBits()

      The 64 most significant bits of the UUID.

      Returns:
      the 64 most significant bits.

    • version

      public int version()

      The version of the variant 2 UUID as per RFC 4122. If the variant is not 2, then the version will be 0.

      • 1 - Time-based UUID
      • 2 - DCE Security UUID
      • 3 - Name-based with MD5 hashing UUID (nameUUIDFromBytes(byte[]))
      • 4 - Randomly generated UUID (randomUUID())
      • 5 - Name-based with SHA-1 hashing UUID
      Returns:
      an int value.

    • variant

      public int variant()

      The variant of the UUID as per RFC 4122.

      • 0 - Reserved for NCS compatibility
      • 2 - RFC 4122/Leach-Salz
      • 6 - Reserved for Microsoft Corporation compatibility
      • 7 - Reserved for future use
      Returns:
      an int value.

    • timestamp

      public long timestamp()

      The timestamp value of the version 1, variant 2 UUID as per RFC 4122.

      Returns:
      a long value.
      Throws:
      UnsupportedOperationException - if version() is not 1.

    • clockSequence

      public int clockSequence()

      The clock sequence value of the version 1, variant 2 UUID as per RFC 4122.

      Returns:
      a long value.
      Throws:
      UnsupportedOperationException - if version() is not 1.

    • node

      public long node()

      The node value of the version 1, variant 2 UUID as per RFC 4122.

      Returns:
      a long value.
      Throws:
      UnsupportedOperationException - if version() is not 1.

    • compareTo

      public int compareTo​(UUID uuid)

      Compares this UUID to the specified UUID. The natural ordering of UUIDs is based upon the value of the bits from most significant to least significant.

      Specified by:
      compareTo in interface Comparable<UUID>
      Parameters:
      uuid - the UUID to compare to.
      Returns:
      a value of -1, 0 or 1 if this UUID is less than, equal to or greater than uuid.

    • equals

      public boolean equals​(Object object)

      Compares this UUID to another object for equality. If object is not null, is a UUID instance, and all bits are equal, then true is returned.

      Overrides:
      equals in class Object
      Parameters:
      object - the Object to compare to.
      Returns:
      true if this UUID is equal to object or false if not.
      See Also:
      Object.hashCode()

    • hashCode

      public int hashCode()

      Returns a hash value for this UUID that is consistent with the equals(Object) method.

      Overrides:
      hashCode in class Object
      Returns:
      an int value.
      See Also:
      Object.equals(java.lang.Object)

    • toString

      public String toString()

      Returns a string representation of this UUID in the following format, as per RFC 4122. 

                  UUID                   = time-low "-" time-mid "-"
                                     time-high-and-version "-"
                                     clock-seq-and-reserved
                                     clock-seq-low "-" node
            time-low               = 4hexOctet
            time-mid               = 2hexOctet
            time-high-and-version  = 2hexOctet
            clock-seq-and-reserved = hexOctet
            clock-seq-low          = hexOctet
            node                   = 6hexOctet
            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 instance.