UUID

About

The UUID (Universally Unique Identifier) class in Java provides a way to generate unique identifiers. It is part of the java.util package and is commonly used in applications where globally unique IDs are required, such as in distributed systems, database keys, or unique identifiers for entities.

• A UUID is a 128-bit value that is highly likely to be unique across all systems and contexts.

• It adheres to the RFC 4122 standard, ensuring consistency and compatibility with other systems that use UUIDs.

• UUIDs are represented as a 36-character string in hexadecimal format, separated into five groups: 8-4-4-4-12 (e.g., 550e8400-e29b-41d4-a716-446655440000).

• Common use cases include identifying resources in a distributed environment, assigning unique database keys, and tagging data entities.

Features

1. Global Uniqueness:

   • Each UUID is designed to be unique, even if generated on different machines or at different times.

2. Different Types of UUIDs:

   • Version 1: Based on timestamp and MAC address.

   • Version 3: Based on a namespace and a name, using MD5 hashing.

   • Version 4: Randomly generated UUIDs.

   • Version 5: Based on a namespace and a name, using SHA-1 hashing.

3. Compact Representation:

   • Despite their uniqueness, UUIDs are compactly represented as a string or a byte array.

4. Thread-Safe:

   • UUID generation methods are thread-safe and can be safely used in multi-threaded environments.

5. Wide Compatibility:

   • UUIDs are widely used across programming languages, databases, and distributed systems.

Declaration

The UUID class is part of the java.util package. To use it, you simply import the class:

import java.util.UUID;

Methods Available

UUID Generation:

• UUID.randomUUID(): Generates a random UUID (Version 4).

• UUID.nameUUIDFromBytes(byte[] name): Generates a UUID based on the specified byte array (Version 3 or 5).

Get UUID Components:

• long getMostSignificantBits(): Returns the most significant 64 bits of the UUID.

• long getLeastSignificantBits(): Returns the least significant 64 bits of the UUID.

UUID Parsing:

• UUID.fromString(String uuid): Creates a UUID from its string representation.

Utility Methods:

• int version(): Returns the version number of the UUID.

• int variant(): Returns the variant number of the UUID.

• String toString(): Converts the UUID to its standard string representation.

• boolean equals(Object obj): Checks if two UUIDs are equal.

• int hashCode(): Returns the hash code of the UUID.

Usage

Basic UUID Generation

import java.util.UUID;

public class UUIDExample {
    public static void main(String[] args) {
        UUID uuid = UUID.randomUUID(); // Generate a random UUID
        System.out.println("Random UUID: " + uuid);
    }
}

Parsing a UUID String

String uuidString = "550e8400-e29b-41d4-a716-446655440000";
UUID uuid = UUID.fromString(uuidString);
System.out.println("Parsed UUID: " + uuid);

Generating UUID from Namespace and Name

import java.util.UUID;

public class UUIDFromNamespaceExample {
    public static void main(String[] args) {
        byte[] nameBytes = "example-name".getBytes();
        UUID uuid = UUID.nameUUIDFromBytes(nameBytes);
        System.out.println("Name-based UUID: " + uuid);
    }
}

Getting UUID Components

UUID uuid = UUID.randomUUID();
System.out.println("UUID: " + uuid);
System.out.println("Most Significant Bits: " + uuid.getMostSignificantBits());
System.out.println("Least Significant Bits: " + uuid.getLeastSignificantBits());
System.out.println("Version: " + uuid.version());
System.out.println("Variant: " + uuid.variant());

Using UUID as a Database Key

public class Entity {
    private String id;

    public Entity() {
        this.id = UUID.randomUUID().toString();
    }

    public String getId() {
        return id;
    }
}

Applications and Real-World Usage

1. Database Keys: UUIDs are often used as primary keys in distributed databases to avoid key collisions.

2. Distributed Systems: Used to identify resources, nodes, or messages uniquely in a network of distributed systems.

3. File or Data Tagging: UUIDs are assigned to files or records for tracking and identification purposes.

4. Session and Token Generation: UUIDs can be used to generate unique session IDs or authentication tokens.

5. Debugging and Logging: UUIDs provide a way to uniquely identify and track events or requests in logs.