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The UUID Class

The java.util.UUID class represents an immutable Universally Unique Identifier (UUID).

A UUID represents a 128-bit value that is unique across both space and time. They are incredibly useful when you need to generate a unique key without coordinating with a central authority (like an auto-incrementing database column).

What does a UUID look like?​

A UUID is typically represented as a 36-character string consisting of 32 hexadecimal digits and 4 hyphens.

Example: 550e8400-e29b-41d4-a716-446655440000

Common Use Cases​

  1. Primary Keys: Generating unique IDs for database records in distributed systems.
  2. Session IDs: Generating unique tokens for user sessions in web applications.
  3. Transaction IDs: Tracking unique requests across microservices.
  4. File Names: Preventing naming collisions when uploading files.

Generating a UUID​

The most common way to generate a UUID in Java is by using the static method UUID.randomUUID(). This generates a Type 4 (pseudo-randomly generated) UUID.

import java.util.UUID;

public class LabUUID1 {

  public static void main(String[] args) {
    // Generate a random UUID
    UUID uniqueKey = UUID.randomUUID();

    // Print the UUID as a String
    System.out.println("Generated UUID: " + uniqueKey.toString());
  }
}

Output:

Generated UUID: 123e4567-e89b-12d3-a456-426614174000

[!TIP] The chance of a collision (generating the exact same UUID twice) using UUID.randomUUID() is so astronomically small that it is considered practically zero. You do not need to check a database to ensure the ID is unique before using it!