UUID (Universally Unique Identifier) is a class in java.util used to create unique identifiers that are 128-bit values, useful in distributed systems, databases, and unique object references.
UUIDs are formatted as:
For example: c9bf9e57-1685-4c89-bafb-ff5af830be8aCommonly Used Constructors and Methods
Simple Program – Generate UUID
import java.util.UUID;
public class SimpleUUIDDemo {
public static void main(String[] args) {
UUID uniqueId = UUID.randomUUID();
System.out.println("Generated UUID: " + uniqueId);
System.out.println("UUID Version: " + uniqueId.version());
System.out.println("UUID Variant: " + uniqueId.variant());
}
}Problem Statement
LotusJavaPrince and Mahesh are managing a distributed document signing system for a digital bank. Each document signed by a customer must be uniquely identified across all branches globally without collisions.
They decide to assign a UUID to each document and store basic info. The system should:
- Generate a UUID for each new document.
- Store document titles with their UUIDs.
- Allow looking up a document by UUID (as string).
- Allow comparison between UUIDs (e.g., for duplicates).
import java.util.*;
class Document {
private UUID id;
private String title;
public Document(String title) {
this.id = UUID.randomUUID();
this.title = title;
}
public UUID getId() {
return id;
}
public String getTitle() {
return title;
}
public void display() {
System.out.println("Document Title: " + title);
System.out.println("Document UUID: " + id);
}
}
public class DocumentManagementSystem {
private static Map<UUID, Document> documents = new HashMap<>();
private static Scanner scanner = new Scanner(System.in);
public static void addDocument() {
System.out.print("Enter document title: ");
String title = scanner.nextLine();
Document doc = new Document(title);
documents.put(doc.getId(), doc);
System.out.println("Document added with UUID: " + doc.getId());
}
public static void lookupDocument() {
System.out.print("Enter UUID to search: ");
String uuidStr = scanner.nextLine();
try {
UUID uuid = UUID.fromString(uuidStr);
Document doc = documents.get(uuid);
if (doc != null) {
doc.display();
} else {
System.out.println("Document not found!");
}
} catch (IllegalArgumentException e) {
System.out.println("Invalid UUID format.");
}
}
public static void main(String[] args) {
while (true) {
System.out.println("\n--- LotusJavaPrince & Mahesh's Document System ---");
System.out.println("1. Add Document");
System.out.println("2. Lookup Document by UUID");
System.out.println("3. Exit");
System.out.print("Choose option: ");
int choice = Integer.parseInt(scanner.nextLine());
switch (choice) {
case 1: addDocument(); break;
case 2: lookupDocument(); break;
case 3: System.exit(0); break;
default: System.out.println("Invalid choice");
}
}
}
}
--- LotusJavaPrince & Mahesh's Document System ---
1. Add Document
2. Lookup Document by UUID
3. Exit
Choose option: 1
Enter document title: CustomerAgreement2025
Document added with UUID: 9d24eeb6-2b19-4d02-8595-2f54c2a4297a
--- LotusJavaPrince & Mahesh's Document System ---
1. Add Document
2. Lookup Document by UUID
3. Exit
Choose option: 2
Enter UUID to search: 9d24eeb6-2b19-4d02-8595-2f54c2a4297a
Document Title: CustomerAgreement2025
Document UUID: 9d24eeb6-2b19-4d02-8595-2f54c2a4297aCode language: PHP (php)The java.util.UUID class provides a reliable, standard way to generate universally unique identifiers in Java. These identifiers are critical in distributed systems, databases, security tokens, and scenarios where uniqueness is paramount.