Java Generate UUID
UUID is a widely used 128-bit long unique identification number in the computer system. It consists of hex-digits separated by four hyphens. In this section, we will discuss what is UUID and how to randomly generate UUID (version 4) in Java.
UUID
UUID stands for Universally Unique IDentifier. UUIDs are standardized by the Open Software Foundation (OSF). It is a part of the Distributive Computing Environment (DCE). A UUID is 36 characters (128-bit) long unique number. It is also known as a Globally Unique IDentifier (GUID).
The use of UUID depends on the situation, use cases, complexity, and conditions. Some of the uses of UUID are:
- It is used to generate unique URN (Uniform Resource Names).
- It can also be used to generate transaction IDs.
- Widely used in a cryptographic application.
- In a web application it can be used to generate session IDs.
Types of UUID
There are four types of UUIDs:
- Time-based UUID (version 1)
- DCE security UUID (version 2)
- Name-based UUID (version 3 and 5)
- Randomly Generated UUID (version 4)
Variants of UUID
There are many variants of the UUID but Leach-Salz variant is widely used. The layout of variant 2 i.e. Leach-Salz is as follows:
The MSBs consists of the following unsigned fields:
0xFFFFFFFF00000000 time_low
0x00000000FFFF0000 time_mid
0x000000000000F000 version
0x0000000000000FFF time_hi
The LSBs consists of the following unsigned fields:
0xC000000000000000 variant
0x3FFF000000000000 clock_seq
0x0000FFFFFFFFFFFF node
The variant field holds a value that identifies the layout of the UUID. The above-discussed layout is valid only for variant 2.
Java UUID Class
For generating the UUID, the Java programming language provides the UUID class. The class belongs to java.util package. It extends the Object class and implements the serializable and comparable<UUID> interface. The class generates an immutable UUID that represents a 128-bit value.
Java UUID Class Methods
| Methods | Description |
|---|---|
| clockSequence() | It returns the clock sequence value associated with this specified UUID. |
| compareTo() | The method compares the UUID with the specific UUID. |
| equals() | The method compares this object to the specified object. |
| fromString() | It generates a UUID from the String representation. |
| getLeastSignificantBits() | It returns the least significant 64 bits of this UUID’s 128-bit value. |
| getMostSignificantBits() | It returns the most significant 64 bits of this UUID’s 128-bit value. |
| hashCode() | It returns a hash code for this UUID. |
| nameUUIDFromBytes() | It retrieves a version-3 (name-based) UUID based on the specified byte array. |
| node() | It returns a node value that is associated with the specified UUID. |
| randomUUID() | It returns a randomly generated UUID. |
| timestamp() | It returns a timestamp value associated with this specified UUID. |
| toString() | It returns a String object representing this UUID. |
| variant() | It is used to get the variant associated with the specified UUID. |
| version() | We can get the version number associated with the specified UUID. |
Generating a UUID
The following example generates a random UUID.
UUIDExample.java
Output:
2b733549-d2cc-40f0-b7f3-9bfa9f3c1b89
Convert from a String to a UUID
StringToUUIDExample.java
Output:
Randomly Generated UUID: fe8a03d7-6495-4231-9843-8ee2f5282620 UUID as String: fe8a03d7-6495-4231-9843-8ee2f5282620 UUID from String: fe8a03d7-6495-4231-9843-8ee2f5282620 true