Picture this: You’re still running Java 8 in production because “it works fine,” but you keep hearing about all the amazing features in newer Java versions. You’re curious, but the thought of upgrading seems daunting. Sound familiar?
If you’re one of the many developers still working with Java 8, you’re not alone. Despite Java 8 reaching end-of-life for free public updates back in 2019, it remains one of the most widely used Java versions in production environments. But here’s the thing: you’re missing out on over six years of improvements, performance gains, and developer productivity features.
Java 21, released in September 2023, is the latest Long-Term Support (LTS) release, and it’s packed with game-changing features. In this post, I’ll walk you through the key differences between Java 8 and Java 21, and make a compelling case for why you should seriously consider upgrading.
Why Java 8 Still Dominates (And Why That’s a Problem)
Java 8 was revolutionary when it launched in 2014. It introduced lambdas, streams, and the new date-time API—features that fundamentally changed how we write Java code. Many organizations adopted it enthusiastically, and… then they stayed there.
The problem? Java 8 hasn’t received free public updates since January 2019. While you can still get commercial support, you’re missing out on:
- Critical security patches
- Performance improvements (we’re talking 30-40% faster in many cases)
- Modern language features that make code cleaner and more maintainable
- Better tooling and debugging capabilities
- Container-aware JVM improvements
Let’s dive into what you’re missing.
The Java Release Cadence: What Changed
Before we compare features, it’s important to understand how Java evolved between version 8 and 21:
- Java 8 (March 2014) - LTS
- Java 9 (September 2017) - Module system introduction
- Java 10 (March 2018) -
varkeyword - Java 11 (September 2018) - LTS
- Java 12-16 (2019-2021) - Feature releases
- Java 17 (September 2021) - LTS
- Java 18-20 (2022-2023) - Feature releases
- Java 21 (September 2023) - LTS
Oracle switched to a six-month release cycle after Java 9, with LTS releases every 2-3 years. Java 21 is the latest LTS, meaning it will receive updates and support for years to come.
Major Language Features You’re Missing
1. Local Variable Type Inference (Java 10)
Remember declaring types everywhere? Java 10 introduced var, making code more concise:
// Java 8
Map<String, List<Customer>> customersByCity = new HashMap<>();
CustomerRepository repository = new CustomerRepositoryImpl();
// Java 10+
var customersByCity = new HashMap<String, List<Customer>>();
var repository = new CustomerRepositoryImpl();While controversial at first, var significantly reduces boilerplate without sacrificing type safety—the compiler still enforces strict typing.
2. Text Blocks (Java 15)
Say goodbye to messy string concatenation for multi-line strings:
// Java 8 - painful
String json = "{\n" +
" \"name\": \"Fernando\",\n" +
" \"role\": \"Software Engineer\",\n" +
" \"location\": \"Spain\"\n" +
"}";
// Java 15+ - beautiful
var json = """
{
"name": "Fernando",
"role": "Software Engineer",
"location": "Spain"
}
""";This is a game-changer for SQL queries, JSON, HTML, and any multi-line text. Your code becomes dramatically more readable.
3. Records (Java 16)
Creating simple data carriers used to require tons of boilerplate:
// Java 8 - so much code for a simple data class
public class Person {
private final String name;
private final int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() { return name; }
public int getAge() { return age; }
@Override
public boolean equals(Object o) {
// ... 15 more lines of boilerplate
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
@Override
public String toString() {
return "Person[name=" + name + ", age=" + age + "]";
}
}
// Java 16+ - one line
public record Person(String name, int age) {}Records automatically generate constructors, getters, equals(), hashCode(), and toString(). They’re perfect for DTOs, API responses, and immutable data structures.
4. Pattern Matching for instanceof (Java 16)
No more casting after type checks:
// Java 8 - redundant casting
if (obj instanceof String) {
String str = (String) obj;
System.out.println(str.toLowerCase());
}
// Java 16+ - pattern matching
if (obj instanceof String str) {
System.out.println(str.toLowerCase());
}Cleaner, safer, and less error-prone.
5. Switch Expressions (Java 14)
The old switch statement was verbose and error-prone. Switch expressions are better:
// Java 8 - classic switch statement
String result;
switch (day) {
case MONDAY:
case FRIDAY:
case SUNDAY:
result = "Long day";
break;
case TUESDAY:
result = "Short day";
break;
default:
result = "Regular day";
}
// Java 14+ - switch expression
var result = switch (day) {
case MONDAY, FRIDAY, SUNDAY -> "Long day";
case TUESDAY -> "Short day";
default -> "Regular day";
};No more forgetting break statements. No more reassigning variables. Just clean, functional-style code.
6. Sealed Classes (Java 17)
Control which classes can extend your class:
// Define a limited hierarchy
public sealed class Shape
permits Circle, Rectangle, Triangle {
}
public final class Circle extends Shape { }
public final class Rectangle extends Shape { }
public final class Triangle extends Shape { }
// This won't compile - Pentagon not permitted
// public final class Pentagon extends Shape { }This is powerful for domain modeling where you want exhaustive pattern matching and a closed set of implementations.
7. Virtual Threads (Java 21) - The Big One
This is arguably the most significant feature in Java 21. Virtual threads make concurrent programming dramatically simpler:
// Java 8 - platform threads are expensive
ExecutorService executor = Executors.newFixedThreadPool(100);
for (int i = 0; i < 10000; i++) {
executor.submit(() -> {
// Handle request
});
}
// Java 21 - virtual threads are lightweight
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 10000; i++) {
executor.submit(() -> {
// Handle request
});
}
}Virtual threads allow you to create millions of threads without the overhead of traditional platform threads. This is perfect for I/O-bound applications, microservices, and concurrent programming.
A simple server example:
// Java 21 - handle each request in its own virtual thread
void serve(ServerSocket serverSocket) throws IOException {
while (true) {
var socket = serverSocket.accept();
Thread.startVirtualThread(() -> handle(socket));
}
}No more complex async/await patterns or callback hell. Just write simple, blocking code that scales.
8. Pattern Matching for Switch (Java 21)
Combine pattern matching with switch for powerful type handling:
// Java 21
static String format(Object obj) {
return switch (obj) {
case Integer i -> String.format("int %d", i);
case Long l -> String.format("long %d", l);
case Double d -> String.format("double %f", d);
case String s -> String.format("String %s", s);
default -> obj.toString();
};
}This makes polymorphic code much cleaner and more maintainable.
9. Sequenced Collections (Java 21)
Finally, a consistent API for collections with a defined order:
// Java 21 - unified interface for ordered collections
SequencedCollection<String> list = new ArrayList<>();
list.addFirst("first");
list.addLast("last");
String first = list.getFirst();
String last = list.getLast();
SequencedCollection<String> reversed = list.reversed();No more confusion about whether LinkedHashSet supports get(0) or whether you need to use Deque methods.
Performance Improvements
Beyond language features, Java 21 brings massive performance improvements:
Garbage Collection
- G1GC improvements: Faster and more predictable
- ZGC: Low-latency garbage collector (sub-millisecond pauses)
- Shenandoah GC: Concurrent GC with minimal pause times
Typical applications see 20-40% performance improvements just from JVM optimizations.
Startup Time
Java 21 starts significantly faster than Java 8, crucial for:
- Serverless functions
- Containerized microservices
- Cloud-native applications
- Development feedback loops
Memory Efficiency
Improvements in memory usage include:
- Compact strings (saves heap memory)
- Better class data sharing
- Improved JIT compilation
- Container-aware memory settings
In containerized environments, Java 21 is much smarter about respecting CPU and memory limits.
Security and Stability
This is critical: Java 8 public updates ended in 2019. Every day you run Java 8 without commercial support, you’re potentially exposed to security vulnerabilities.
Java 21 includes:
- Years of security patches
- Hardened cryptography
- Improved security manager (though deprecated, better alternatives exist)
- Modern TLS support
- Better protection against known attack vectors
API Improvements
Hundreds of API improvements make development more productive:
HTTP Client (Java 11)
// Java 8 - use third-party libraries or HttpURLConnection (ugly)
// Java 11+ - modern, built-in HTTP client
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create("https://api.example.com/data"))
.build();
HttpResponse<String> response = client.send(request,
HttpResponse.BodyHandlers.ofString());Collection Factory Methods (Java 9)
// Java 8
List<String> list = Arrays.asList("a", "b", "c");
Map<String, Integer> map = new HashMap<>();
map.put("a", 1);
map.put("b", 2);
// Java 9+
var list = List.of("a", "b", "c");
var map = Map.of("a", 1, "b", 2);Stream Improvements
New methods like takeWhile(), dropWhile(), ofNullable(), and iterate() make streams more powerful:
// Get first 5 positive numbers
Stream.iterate(1, n -> n + 1)
.takeWhile(n -> n <= 5)
.forEach(System.out::println);Optional Improvements
// Java 9+ - stream from Optional
optional.stream()
.filter(...)
.map(...)
.collect(Collectors.toList());
// Java 10+ - orElseThrow without arguments
String value = optional.orElseThrow();
// Java 11+ - isEmpty check
if (optional.isEmpty()) {
// handle absence
}Why You Should Upgrade to Java 21 (Not Just 17)
You might be thinking: “Why not just upgrade to Java 17 (the previous LTS)?” Valid question. Here’s why Java 21 is worth it:
- Virtual Threads: Alone worth the upgrade for server applications
- Pattern Matching for Switch: Makes code significantly cleaner
- Sequenced Collections: Fills a long-standing API gap
- Longer Support: More years of updates than Java 17
- Performance: Additional optimizations over Java 17
- Future-Proof: Better foundation for future Java versions
Migration Considerations
I won’t sugarcoat it: upgrading from Java 8 to Java 21 requires work. But it’s manageable:
1. Module System (Optional)
Java 9 introduced the module system, but you don’t have to modularize your application. The classpath still works fine.
2. Removed APIs
Some deprecated APIs were removed:
Thread.stop(),Thread.destroy()- use interrupts instead- Some CORBA and Java EE modules - now separate libraries
- Nashorn JavaScript engine - use GraalVM instead
3. Dependency Updates
Update your dependencies to Java 11+ compatible versions:
- Spring Boot: 3.x supports Java 17+
- Hibernate: 6.x for Java 17+
- Most libraries have Java 11+ versions by now
4. Build Tools
Update Maven/Gradle and plugins:
<!-- Maven -->
<properties>
<maven.compiler.source>21</maven.compiler.source>
<maven.compiler.target>21</maven.compiler.target>
</properties>// Gradle
java {
toolchain {
languageVersion = JavaLanguageVersion.of(21)
}
}The Bottom Line: Should You Upgrade?
Absolutely yes. Here’s my recommendation:
✅ Upgrade if you’re:
- Running production systems on Java 8
- Building new applications
- Concerned about security
- Looking for performance gains
- Wanting modern development features
⚠️ Consider waiting if:
- You have a critical system with no test coverage (fix that first!)
- Your dependencies don’t support Java 11+ yet (rare these days)
- You’re in a regulated industry with slow approval processes (start now!)
My Personal Experience
I’ve been part of several Java 8 → 17/21 migrations, and every single one resulted in:
- Better performance (typically 25-35% improvement)
- Happier developers (modern features are productive)
- Reduced bugs (better language features = safer code)
- Lower cloud costs (better resource usage)
The migration effort pays off quickly. In one project, virtual threads alone reduced our server count by 40% while improving response times.
Getting Started Today
Don’t wait for the perfect moment. Start small:
- Install Java 21 using SDKMAN (see my SDKMAN guide)
- Create a spike branch and try compiling your project
- Experiment with new features in a sandbox project
- Build a migration plan and get stakeholder buy-in
- Start migrating one service/module at a time
Conclusion
Java 21 isn’t just an incremental update—it’s a generational leap from Java 8. With virtual threads, pattern matching, records, text blocks, and countless performance improvements, it fundamentally changes how we write Java applications.
Yes, migration requires effort. Yes, you’ll need to update dependencies and possibly refactor some code. But the benefits—security, performance, developer productivity, and future-proofing—far outweigh the costs.
Java 8 had a good run, but it’s 2025. It’s time to move forward.
If you’re still on the fence, start with a proof of concept. Install Java 21, compile your project, run your tests, and see what breaks. You might be surprised how smooth the transition can be.
What’s your Java version story? Still on 8? Already on 21? Running into migration challenges? I’d love to hear about your experiences!