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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

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

df6fdea1-10c3-474c-ae62-e63def80de0b


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

UUID Constructor

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

```

Constructs anew `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 aUUID 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 version3 (name based)UUID based on the specifiedbyte array.

```java

UUID.randomUUID()

```

This method is used to create a version4 (pseudo randomly generated)UUID.

###Instance methods

Also there are a few instance methods of aUUID class.

```java

clockSequence()

```

This method is used to get the the clock sequence value associated withthisUUID.

This method returns the clock sequence value as `int`.

```java

compareTo(UUID val)

```

This method is used to comparethisUUID with the specifiedUUID ( the one received as method param i.e. `val`

This method returns-1,0 or1 asthis `UUID` is less than, equal to, or greater than `val`

```java

equals(Object obj)

```

This method simply comparesthis object to the specified object.Itreturn the result in `boolean`

```java

node()

```

This method returns the node value (`long`) associated withthisUUID.

```java

timestamp()

```

This method returns the timestamp value (`long`) associated withthisUUID.

```java

toString()

```

This method returns a `String` object representingthisUUID.

```java

variant()

```

This method returns the variant number (`int`) associated withthisUUID.

```java

version()

```

This method returns the version number (`int`) associated withthisUUID.

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.

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