What's New in Java 21 [Key Changes to Know]

Java, the most popular software development platform, has been evolving continuously. From version to version, each time, it brings in copious changes and improvements. Java 21 is one such iteration with some new features. It also features several improvements that will make working with Java fun.

You will have new APIs, performance improvements, better Java Flight Recorder, improved pattern, and so on in its latest iteration, and many more exciting improvements. 

What is new in these changes? How can it be compared with the previous version, Java 17? Well, that's what this article is meant to consider. This is just a brief summary of some exciting new features. Comparison with Java 17 will also be made. So, let us get started upon this journey investigating into the prime changes in Java 21. Do you want to update to Java 21, here's how you can update Java JDK to use Java 21.  

There is quite a difference between Java 17 and 21. The new version touts better features, more enhanced APIs, and performance improvements. Java 21 brings a fresh experience to developers, keeping up with agile development methodologies. These updates refine existing features, making Java 21 a versatile language. They are intended to target some developer pain points and also to enhance the code maintainability aspect. Java 21 includes:

• Enhanced switch expressions for more concise code.

• Expansion of pattern matching capabilities.

• Introduction of new APIs for more efficient development.

Java 21 Release Date

September 19, 2023 was the formal release date of Java 21.

Java 21 vs Java 17: A Comparative Overview

Java 21 is the next platform improvement over Java 17. Java 17 was a great LTS release, which meant, to a certain extent, that Java 21 has taken the game forward. Overall, one of the highlighted advancements in Java 21 is improved syntax. Now it has become more easier to write cleaner code. A lot of the previous versions already contributed in that direction.

However, the new features will provide additional tools that developers can use.

Another one, Records, which we have seen in Java 17. It now supports immutable data patterns. You now have a better alternative to traditional classes. Coming to performance improvement, you will find Java applications are more efficient in memory management. Java 21 includes refined garbage collection algorithms. 

By far, this is the most important jump for Java 21 to take from Java 17: cloud-native and microservice architectures. These optimizations are vital to systems designed for distributed environments. Here's a quick comparison of key aspects between Java 17 and Java 21:

• Java 21 brings more syntax improvements

• Improved garbage collection and performance tuning

• Java 21 offers better support for microservices

• The expanded API offerings

Ultimately, Java 21 ups its game with an extremely powerful base of version 17. It brings cool features for modern-day software developers.

With ever-changing coding paradigm, Java is transitioning into a more flexible programming language. Language improvement is one of the crucial improvements with this update.  You will find a wealth of new libraries. They are to assist them in handling complex processes more efficiently.

Advanced garbage collection techniques, another great addition. When working with resource intensive environments, they improve application performance. As usual, data protection and privacy remain the top priority in this update too. Many changes have transformed Java into a more secure platform for sensitive applications. Overall, though, this edition offers developers far more flexibility and productivity.  

So here are the major additions to the platform Java 21 defined: 

• Enhanced Syntax

• New Libraries for Different Tasks 

• Improved Memory Management 

• New Cryptographic Features and Modules 

• New Tools for Developers 

Let's break down these advancements in detail.

1. Language Enhancements and Syntax Improvements

Modern syntax, which was born in Java 17, enables even more current programming styles at their best.

Sealed Classes (Java 17): Provides a clear, restricted inheritance hierarchy.

Pattern Matching for switch (Java 21): Simplifies code readability by combining type checks and destructuring in a concise syntax.

Example: Sealed Classes (Java 17) Enhanced with Pattern Matching for switch (Java 21)

sealed interface Vehicle permits Car, Truck {}

 

record Car(String brand, int speed) implements Vehicle {}

record Truck(String brand, double loadCapacity) implements Vehicle {}

 

public class Java21ModernSyntax {

    public static void main(String[] args) {

        Vehicle myVehicle = new Truck("Volvo", 15.5);

 

        // Java 21 - Enhanced with Pattern Matching for Switch

        String details = switch (myVehicle) {

            case Car(String brand, int speed) -> "Car: " + brand + ", Speed: " + speed + " km/h";

            case Truck(String brand, double loadCapacity) -> 

                "Truck: " + brand + ", Load Capacity: " + loadCapacity + " tons";

        };

 

        System.out.println(details);

    }

}

Why It Matters

1. What started with sealed classes in Java 17 is now paired with the power of pattern matching in Java 21.

2. Java now enforces type safety and eliminates repetitive boilerplate code.

3. These enhancements make Java more competitive for building modern, maintainable applications.

The other improvement to switch expressions not only makes them more versatile but also easier to work with, improving the decision-making processes that streamline the flow of decision-making in code logic.

Example: Enhanced switch Expressions in Java 21

sealed interface Animal permits Dog, Cat, Bird {}

 

record Dog(String name) implements Animal {}

record Cat(String name, int livesLeft) implements Animal {}

record Bird(String species, double wingspan) implements Animal {}

 

public class SwitchEnhancements {

    public static void main(String[] args) {

        Animal myPet = new Cat("Whiskers", 9);

 

        // Java 21 - Enhanced switch expressions

        String description = switch (myPet) {

            case Dog(String name) -> "This is a dog named " + name;

            case Cat(String name, int livesLeft) -> "A cat named " + name + " with " + livesLeft + " lives left";

            case Bird(String species, double wingspan) -> "A bird of species " + species + " with a wingspan of " + wingspan + " meters";

        };

 

        System.out.println(description);

    }

}

 

Improving data types and providing new syntactic options form a lot more into the ordinary programming environment, whereas eliminating extra lines of code increases clarity in certain cases. 

With these enhancements, Java 21 creates a smoother, more modern programming experience. By enabling intuitive, clear, and elegant code, these updates bring real-world benefits to all developers, streamlining logic and boosting productivity.

2. New APIs and Libraries

The introduction of Java 21 has brought along a number of promising new APIs and libraries meant for specific problem scenarios in development. The versatility and effectiveness of the language have, therefore, just increased.

The most prominent of the Java 21 features is the enhanced Streams API, placing Java at par in the row of languages that promise competitive processing of enormous data.

Addition of new networks- now it really adds up to set up an impressive foundation for developing scalable applications on the network. Very essential upgrades in this kind of environment are really important to any cloud-based and distributed system.

In addition, there are libraries in Java 21 for new-age data structures even more amenable to modern needs in feeding different types of data efficiently and effectively.

These changes are indicative of the fact that Java is still very much capable of serving the best users for a wide range of applications-from enterprise solutions down to real-time systems-just because of the richer capabilities of its diverse libraries.

1. Enhanced Streams API Simplifies data processing with new methods like takeWhile and dropWhile for better control.

2. Sequenced Collections Introduces a new interface for collections with a defined iteration order, supporting easy manipulation like reversing.

3. Key Encapsulation Mechanism (KEM) API Provides secure cryptographic key exchange, critical for distributed and cloud systems.

4. Scoped Values, a safer and faster alternative to ThreadLocal, enabling better context management in multi-threaded applications.

5. Structured Concurrency (Incubator) Treats related concurrent tasks as a single unit, simplifying error handling and resource management.

6. Foreign Function and Memory API (Preview) Allows safer and easier interaction with native code and memory outside the JVM.

7. Vector API (Incubator) Offers improved performance for vector computations in data-heavy applications.

8. String Templates (Preview) Simplifies the creation of dynamic strings with placeholders, making string concatenation more readable.

9. Unnamed Patterns and Variables Streamlines code readability by allowing placeholders for unused pattern variables.

10. Unnamed Classes and Instance Main Methods Simplifies the creation of throwaway classes for quick tests and experiments.

11. Generational Z Garbage Collector (ZGC) Enhances performance and reduces latency for memory-intensive applications.

3. Performance and Garbage Collection Enhancements

Two new JVM garbage collection modes introduced in Java 21 are for reduced latency and improved throughput for applications. This really pays off for high-demand applications.

Optimized memory allocation comes with reduced pause time and a more predictable application footprint. 

Along with the already present improvements in performance through better concurrent process support, performance enhancements in Java 21 will further strengthen the ability of the language to provide a robust environment for effectively handling multi-threaded applications.

3. Security and Privacy Upgrades

It has important updates for the security and privacy features of Java. Now enhanced cryptographic algorithms will provide better security for the data encryption and transmission. These will protect the sensitive information worldwide.

Privacy feature improvements include invulnerable access and data management controls for preventing unauthorized access to data. Such accesses are very damaging in applications dealing with personal and sensitive information.

In general, with these improvements in Java 21, the servers and individuals would have the right tools to design applications that are much more secured in this hostile digital space.

Deprecated Features and APIs in Java 21

Java 21 has kept up with the vales of deprecating older or non-standardized features as well as APIs. This has maintained the upkeep of the language and continuous improvement of code quality.

At the heart of Java 21 is the retirement of obsolete elements, those that may create security risks or prevent other new developments. That push is meant to use newer and more efficient examples for Java developers.

Here’s a concise summary of the deprecated and removed features in Java from versions 18 to 21.

1. Finalization: It was unreliable and caused resource management issues.

2. Locales: Transition to static factory methods for consistency.

3. COMPAT Locale Provider: Warning added for the use of the COMPAT locale provider (JDK 19, JDK-8304982).

4. JAR Index Feature: It was an outdated optimization for applets, which are now obsolete.

Factors to Consider when Migrating from Java 17 to Java 21

Migration from Java 17 to Java 21 takes place by putting strategic thinking into it to bring about successful transitions. Compatibility clearly stands out as a key issue. The fact that Java 21 comes with changes means that it is a relevant factor for all existing codebases.

Java21 ensures backward compatibility in most features, but tense attention should be paid to deprecated APIs along with updates to see their potential impacts to maintain the code's functionality and performance.

Testing in a migration process becomes a significant issue. Effective and efficient testing leads to the early detection of issues, enabling developers to answer very early about compatibility problems to prevent disruptions while increasing reliability at upgrade times.

Tooling support in Java 21 is enhanced to assist developers in refactoring and upgrading their projects. Using such tools improves the productivity of the migration process by saving time and reducing errors.

All these things ensure that careful planning and compliance with guidelines given in Java 21 would make productive even all those latest advantages without compromising the integrity of the system. This effectively enables organizations to leverage the improvements and advantage in project delivery.

Upgrade Challenges

• Conflicts with external implementations of collection interfaces.
• Deprecated or removed APIs like Thread.stop and Thread.suspend for Loom readiness.
• Security Manager is being phased out, requiring alternative security checks.
• Finalization deprecated; replace with try-with-resources or cleaners.
• Changes in network interface naming and stricter URL parsing may break existing workflows.
• Idle connection timeout for the HTTP Client is now configurable but stricter by default.
• Transition to Unicode CLDR 42 introduces changes in date/time formatting and number systems.
• Libraries like Mockito may trigger warnings due to dynamic agent loading changes.