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+---
+layout: post
+title: "Your Guide To UUID In Java"
+author: gaurav
+image: assets/images/2020-12-19/uuid.png
+categories: [ Java, Core Java, String]
+description: In this article you will learn what is UUID and about the Java UUID class.
+featured: false
+
+---
+
+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 the variant 2 is used.
+
+UUID can be used in the following cases
+ 
+ -  As a primary key of database table
+-   To create session id for web application
+-   To represent as transaction id
+-   To create a random file name
+
+### Example UUID
+
+df6fdea1-10c3-474c-ae62-e63def80de0b
+
+![Structure of UUID](/assets/images/2020-12-19/uuid.png)
+## Java UUID class
+
+UUID Class belongs to the `java.util` package. It represents an immutable universally unique identifier (UUID).
+
+UUID Constructor
+
+```java
+`[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,
+
+```java
+UUID.fromString(String name) 
+```
+The above method creates a UUID from the string standard representation as described in the [toString()](https://docs.oracle.com/javase/8/docs/api/java/util/UUID.html#toString--) method.
+
+```java
+UUID.nameUUIDFromBytes(byte[] name) 
+```
+This method is used to create a version 3 (name based) UUID based on the specified byte array.
+
+```java
+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.
+
+```java 
+clockSequence()
+```
+This method is used to get the the clock sequence value associated with this UUID.
+
+This method returns the clock sequence value as `int`.
+
+```java
+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`
+
+```java
+equals(Object obj)
+```
+This method simply compares this object to the specified object. It return the result in `boolean`
+
+```java
+node()
+```
+This method returns the node value (`long`) associated with this UUID.
+
+```java
+timestamp()
+```
+This method returns the timestamp value (`long`) associated with this UUID.
+
+```java
+toString()
+```
+This method returns a `String` object representing this UUID.
+
+```java
+variant()
+```
+This method returns the variant number (`int`) associated with this UUID.
+
+```java
+version()
+```
+This method returns the version number (`int`)  associated with this UUID.
+
+--------
+You can visit my [YouTube channel 'coderolls'](https://www.youtube.com/channel/UCl31HHUdQbSHOQfc9L-wo3w?view_as=subscriber?sub_confirmation=1) to find more video tutorials.
+
+If you found this article worth, support me by  [giving a cup of Coffee ☕](https://www.paypal.me/GauravKukade)
+
+#### Related Articles
+
+-   [Learn About Java String Pool And intern() Method](https://coderolls.com/java-string-pool-and-intern-method/)
+-   [How Do I Compare Strings In Java](https://coderolls.com/compare-strings-in-java/)
+-   [How To Reverse A String In Java (5 ways)](https://coderolls.com/reverse-a-string-in-java/)
+-   [Compare Two Strings Lexicographically In Java](https://coderolls.com/compare-two-strings-lexicographically-in-java/)
+-   [Introduction to Java Technology (Language and Platform)](https://coderolls.com/java-introduction/)
+