Your Guide To UUID In Java

In this article, we will see,

• What is UUID?
• Java UUID class

What is UUID?

UUID, a universally unique identifier is a 128-bit number used to identify information in computer systems.

UUID is made of hex digits along with 4 hyphen (“-“) symbols. The length of a UUID is 36 characters.

There are 4 types of UUID

1. Time-based UUID (Version 1)
2. DCE Security UUID (Version 2)
3. Name-based UUID (Version 3 and 5)
4. Randomly Generated UUID (Version 4)

Mostly Randomly Generated UUID i.e. UUID Version 4 is used.

UUID Version 4 uses random numbers as a source. It uses an unpredictable value as the seed to generate random numbers to reduce the chance of collisions

There are 4 types of UUID variant

• 0: It is reserved for NCS backward compatibility
• 2: Leach-Salz
• 6: It is reserved for Microsoft backward compatibility
• 7: It is reserved for future definition.

Mostly variant 2 is used.

UUID can be used in the following cases

• As a primary key of the database table
• To create a session ID for a web application
• To represent as transaction ID
• To create a random file name

Example UUID

df6fdea1-10c3-474c-ae62-e63def80de0b

Java UUID class

UUID Class belongs to the java.util package. It represents an immutable universally unique identifier (UUID).

UUID Constructor

1
`[UUID](https://docs.oracle.com/javase/8/docs/api/java/util/UUID.html#UUID-long-long-)(long mostSigBits, long leastSigBits)`

Constructs a new UUID using the specified data.

Static methods

There are three static methods of a UUID class,

1
UUID.fromString(String name) 

The above method creates a UUID from the string standard representation as described in the toString() method.

1
UUID.nameUUIDFromBytes(byte[] name) 

This method is used to create a version 3 (name-based) UUID based on the specified byte array.

1
UUID.randomUUID()

This method is used to create a version 4 (pseudo-randomly generated) UUID.

Instance methods

Also, there are a few instance methods of a UUID class.

1
clockSequence()

This method is used to get the clock sequence value associated with this UUID.

This method returns the clock sequence value as int.

1
compareTo(UUID val)

This method is used to compare this UUID with the specified UUID ( the one received as method param i.e. val

This method returns -1, 0 or 1 as this UUID is less than, equal to, or greater than val

1
equals(Object obj)

This method simply compares this object to the specified object. It returns the result in boolean

1
node()

This method returns the node value (long) associated with this UUID.

1
timestamp()

This method returns the timestamp value (long) associated with this UUID.

1
toString()

This method returns a String object representing this UUID.

1
variant()

This method returns the variant number (int) associated with this UUID.

1
version()

This method returns the version number (int) associated with this UUID.

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