UUID

UUID

java.util

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Java 5.0

serializable comparable

This class is an immutable representation of 128-bit Universal Unique Identifier, or UUID, which serves as an identifier that is (with very high probability) globally unique. Create a UUID based on random bits with the randomUUID( ) factory method. Create a UUID based on the MD5 hash code of an array of bytes with the nameUUIDFromBytes( ) factory method. Or create a UUID by parsing a string with the fromString( ) factory method. The standard string format of a UUID is 32 hexadecimal digits, broken into five hyphen-separated groups of 8, 4, 4, 4, and 12 digits. For example:

 7cbf3e1a-d521-40ac-87f1-e28b17530f60 

Both lowercase and uppercase hex digits are allowed. The toString( ) method converts a UUID object to a string using this standard format. You can also create a UUID object by explicitly passing the 128 bits in the form of two long values to the UUID( ) constructor, but this option should be used only if you are intimately familiar with the relevant UUID standards.

The toString( ) and equals( ) methods define the most common operations on a UUID. The UUID class implements the Comparable interface and defines an ordering for UUID objects. Note, however, that the ordering does not represent any meaningful property, such as generation order, of the underlying bits.

Various accessor methods provide details about the bits of a UUID , but these details are rarely useful. getLeastSignificantBits( ) and getMostSignificantBits( ) return the bits of a UUID as two long values. version( ) and variant( ) return the version and variant of the UUID, which specify the type (random, name -based, time-based) and bit layout of the UUID. timestamp( ) , clockSequence( ) , and node( ) return values only for time-based UUIDs that have a version( ) of 1. Note that the UUID class does not provide a factory method for creating a time-based UUID.

Figure 16-67. java.util.UUID

 public final class  UUID  implements Serializable, Comparable<UUID> {  // Public Constructors  public  UUID  (long  mostSigBits  , long  leastSigBits  );  // Public Class Methods  public static UUID  fromString  (String  name  );        public static UUID  nameUUIDFromBytes  (byte[ ]  name  );        public static UUID  randomUUID  ( );  // Public Instance Methods  public int  clockSequence  ( );        public long  getLeastSignificantBits  ( );        public long  getMostSignificantBits  ( );        public long  node  ( );        public long  timestamp  ( );        public int  variant  ( );        public int  version  ( );  // Methods Implementing Comparable  public int  compareTo  (UUID  val  );  // Public Methods Overriding Object  public boolean  equals  (Object  obj  );        public int  hashCode  ( );        public String  toString  ( );   }