UUID Class

1. Introduction

UUID stands for Universally Unique Identifier.

In Java, the UUID class is available in:

java.util.UUID

It is used to generate unique identifiers that are extremely unlikely to duplicate.

UUIDs are commonly used in:

• Database primary keys
• Distributed systems
• Microservices
• Session identifiers
• API tokens
• Order IDs

2. What Is a UUID?

A UUID is a 128-bit number represented as a 36-character string.

Example:

550e8400-e29b-41d4-a716-446655440000

Structure:

8-4-4-4-12 characters (hexadecimal)

It contains:

• Letters (a–f)
• Numbers (0–9)
• Hyphens separating sections

3. Why UUID Is Important

In distributed systems:

• Multiple servers generate IDs
• There is no central authority
• Auto-increment IDs can collide

UUID solves this by generating IDs that are:

• Practically unique
• Globally unique
• Safe across systems

It avoids database bottlenecks caused by sequential IDs.

4. Generating Random UUID

Most common way:

import java.util.UUID;

UUID id = UUID.randomUUID();
System.out.println(id);

Output example:

c9b1d7f4-3f23-4b8e-9c0f-5b9f1234abcd

Each time you run, a different value is generated.

5. Converting UUID to String

UUID id = UUID.randomUUID();
String value = id.toString();

System.out.println(value);

UUID is commonly stored as String in:

• Databases
• JSON responses
• API payloads

6. Creating UUID from String

If you already have UUID in string form:

String str = "550e8400-e29b-41d4-a716-446655440000";

UUID id = UUID.fromString(str);
System.out.println(id);

If the string is invalid format, it throws:

• IllegalArgumentException

7. UUID Version Concept

UUID has different versions.

The most commonly used in Java:

• Version 4 → Random-based UUID

UUID.randomUUID() generates Version 4 UUID.

You can check version:

UUID id = UUID.randomUUID();
System.out.println(id.version());

Output:

4

8. Getting Most and Least Significant Bits

Internally UUID is stored as two long values:

UUID id = UUID.randomUUID();

long most = id.getMostSignificantBits();
long least = id.getLeastSignificantBits();

System.out.println(most);
System.out.println(least);

Used in:

• Low-level systems
• Performance-optimized storage

9. UUID in Databases

Instead of:

id INT AUTO_INCREMENT

You can store:

id VARCHAR(36)

Or in modern databases:

id UUID

Advantages:

• No collision across systems
• Safer in distributed architecture

Disadvantages:

• Larger storage size
• Not sequential (affects index performance)

10. UUID vs Auto-Increment ID

Use UUID when:

• System is distributed
• IDs must not be predictable
• Security matters

11. Practical Example: Generating Order ID

import java.util.UUID;

class Order {
    private String orderId;

    public Order() {
        this.orderId = UUID.randomUUID().toString();
    }

    public String getOrderId() {
        return orderId;
    }
}

public class Main {
    public static void main(String[] args) {
        Order order = new Order();
        System.out.println(order.getOrderId());
    }
}

Each order will have a unique ID.

12. Summary

• UUID is in java.util.
• Represents a 128-bit unique identifier.
• Generated using UUID.randomUUID().
• Commonly used in distributed systems and databases.
• Version 4 UUID is random-based.
• Stored as String or native UUID type in database.
• Provides global uniqueness with minimal collision risk.

Written By: Shiva Srivastava