Guide on Java 21 and Java 17: Which One to Choose?

Since the Java platform has switched to a six-month release cycle, we’ve moved past the age-old questions, ‘Will this be Java’s last year?’ or ‘Is it worth migrating to the new version?’

Despite 28 years since the launch of its first version, Java continues as a popular primary option for programming language for many new projects. Besides, the platform keeps improving with every new launch. For instance, Java 17 was a significant milestone at its launch. However, that system has now been replaced by Java 21 as the next long-term support release (LTS). 

While Java 21 is an update to 17, it shares several elements that confuse developers. Therefore, in this blog, we’ll examine the differences between Java 21 and 17 to determine which version is better. 

So continue reading as we learn more about the different versions of the program in the following sections of the blog. 

Java 17 & 21 – Explained in Depth

Java 17 and Java 21 are breakthrough moments in Java’s growth, offering significant improvements over its previous generations for developers. Java 17, published in September 2021 as a Long-Term Support (LTS) version, prioritized stability by providing sealed classes for better inheritance control. It focused on improving random number generators, previewing pattern matching for switch statements, and removing obsolete APIs and components. These enhancements gave Java developers a more safe and efficient base for developing applications, making Java 17 a viable option for long-term projects.

This was followed by the launch of Java 21, which was released two years later, in September 2023. Much like 17, 21 was also a revolutionary launch with features aimed at contemporary application development. Java 21 had virtual threads as its key improvement, simplifying concurrency by enabling more scalable and resource-efficient programs. The update also included sequenced collections for easier handling of ordered data and standardized pattern matching for switches, which improved code readability and flexibility. 

Together, Java 17 and Java 21 demonstrate Java’s dedication to dependability, performance, and developer productivity, ensuring that it remains the top choice for contemporary software solutions. Now that we know the two versions, let’s learn more about their core features in the next section. 

Core Features of Java 17

Sealed Classes

Sealed classes offer a unique technique for defining class hierarchies. By limiting which classes can inherit from a sealed class, developers get more control over the subclassing structure, resulting in a more predictable and secure architecture. This is especially handy for API developers who wish to restrict the expansion of specific classes to a subset of subclasses.

Enhanced Random Number Generators

With Java 17, random number generation is more reliable and configurable. New interfaces and classes for generating random numbers enable developers to fine-tune random sequences and increase the efficiency of randomness-based algorithms, making them more appropriate for a wider range of applications.

Pattern Matching for Switch (Preview)

Pattern matching, for example, was first introduced and is currently accessible as a trial feature in switch statements. It makes code more expressive and understandable by letting conditions be evaluated immediately within the switch statement, thus minimizing boilerplate code.

Removal of Deprecated APIs and Components

Java 17 continues to improve the Java platform by eliminating old APIs and components. By deprecating and deleting old parts, Java 17 simplifies the platform, minimizes maintenance needs, and promotes best practices.

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Core Features of Java 21

Virtual Threads (Project Loom)

Virtual threads simplify concurrency management by creating lightweight threads that handle thousands of concurrent processes. This functionality is perfect for scaling applications with high concurrency requirements, decreasing the load on system resources while maintaining performance and responsiveness.

Sequenced Collections

Sequenced collections support ordered collections, allowing for easy retrieval and change depending on insertion order. This feature enhances data management in lists, sets, and maps by offering a straightforward approach to handling ordered items, increasing code clarity and sequence efficiency.

String Templates

String templates allow you to incorporate expressions directly into strings, simplifying string handling by eliminating the requirement for concatenation. This feature improves code clarity, reduces syntax mistakes, and improves dynamic string handling efficiency, making it ideal for applications requiring substantial text processing.

Record Patterns & Pattern Matching for Switch (Standardized)

Standardizing record patterns and switch pattern matching increases code clarity and conciseness, particularly for complicated data structures. It allows for more flexible data handling in switch statements, making Java more expressive and appropriate for functional programming patterns.

Foreign Function & Memory API

This API allows Java programs to work smoothly with native libraries and manage memory outside the JVM. It is beneficial for performance-intensive applications, allowing Java to safely interact with non-Java code while also improving Java’s skills in systems and high-performance development.

Performance Enhancements Over Java 17 & 21

Java 17 Enhancements

Java 17 is a Long-Term Support release that prioritizes stability while providing functional program improvements. It improved memory management and garbage collection with G1 and ZGC improvements, allowing Java programs to handle more data while decreasing latency, particularly in memory-intensive workloads. 

These advancements made Java 17 a reliable alternative for organizations wanting robust, optimized performance with minimum maintenance overhead. It is suited for production situations that require dependability and improved resource management.

Java 21 Enhancements

Java 21 introduced virtual threads as a part of its Project Loom. This new update focuses on revolutionizing concurrency by allowing lightweight thread management with substantially lower overhead. Unlike regular threads, virtual threads significantly increase performance in high-concurrency applications by reducing resource consumption, making them perfect for cloud-native and microservices architectures. 

Additionally, the Foreign Function & Memory API streamlines native code interactions and bypasses the requirement for expensive interoperability layers. Java 21’s performance enhancements prioritize scalability, making it ideal for resource-efficient, contemporary mobile application development.

Benefits of Java 21 – What Does the System Adds for Organizations

Improved Concurrency Handling

Java 21 adds virtual threads, revolutionizing concurrency by allowing thousands of lightweight threads without the performance penalty associated with regular threads. Virtual threads, part of Project Loom, make managing concurrent processes easier, especially in online applications and cloud-native settings. This feature enhances scalability and resource efficiency, allowing developers to design high-throughput applications capable of handling large workloads without complicated thread management.

Enhanced Developer Productivity 

Java 21 boosts efficiency with string templates and record patterns, which improve code readability and decrease boilerplate. Record patterns simplify data extraction inside records, allowing for simple matching logic. String templates simplify how strings are handled, providing a more elegant syntax for inserting expressions directly into strings. Together, these capabilities speed up development by reducing repetitious code and making complicated data structures easier to manage.

Advanced API Integrations

The Foreign Function and Memory API in Java 21 makes dealing with native code safer and more efficient. This API makes it easier for Java programs to use non-Java libraries, lowering the risk of memory leaks and pointer mistakes. This feature allows developers to construct high-performance programs communicating with native libraries while benefiting from better safety checks, increasing dependability in mixed-language development.

Better Performance

With garbage collection and memory management enhancements, Java 21 allows programs to handle greater workloads more effectively. Enhancements to the ZGC and G1 collectors minimize latency and increase throughput, making Java suited for high-performance applications. Optimized memory handling reduces delays and increases responsiveness, critical for real-time and large-scale applications. These innovations enable Java programs to expand while offering quick, smooth performance in demanding contexts.

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Strengthened Security

Java 21 prioritizes security through regular upgrades that improve compliance with industry standards and guard against vulnerabilities. Patches are issued regularly to solve possible exploits, while runtime and library security upgrades provide additional protection. This emphasis on security offers developers confidence in Java’s ability to handle safe applications, making it a strong choice for corporate and regulatory-sensitive contexts, such as financial and healthcare apps.

How Can Organizations Upgrade to Java 21?

Upgrading to the latest version of Java (version 21) from an older version (such as Java 17) is simple. It requires a structured approach to minimize downtime, ensure compatibility, and maximize benefits. 

Here’s a step-by-step approach to how organizations can upgrade to the latest version of Java. 

Step I: Assessment and Planning

The first stage is to perform a thorough assessment to identify compatibility concerns and develop a plan for the update. Start by examining the release notes and deprecations for Java 21 and analyzing the current codebase to identify places that may require changes. Create a clear upgrade strategy that outlines critical stages, resources, and dates to help avoid surprises during the changeover.

Step II: Environment Setup 

Once the planning is complete, build up discrete development and testing environments that are identical to the production setup but operate on Java 21. This isolated environment enables the team to securely test the codebase, ensuring that any flaws are corrected before it reaches production. A properly built testing environment allows developers to experiment with new Java 21 capabilities without disrupting operations.

Step III: Codebase Testing  

With the environments in place, start testing the codebase. Look for deprecated methods or APIs that may no longer be supported in Java 21, and rework the code accordingly. Run unit and integration tests to look for problems with performance or functionality, paying special attention to concurrency and threading, as these areas frequently fail during Java upgrades. This step guarantees that the program runs properly with the Java 21 features.

Step IV: Training and Documentation  

Introducing Java 21 to your business may result in substantial feature changes. Hold training sessions to introduce the team to new features such as virtual threads, record patterns, and increased API possibilities. Additionally, documentation should be updated to reflect changes in the codebase and discuss best practices for Java 21. This stage allows the team to use Java 21’s benefits efficiently while maintaining code quality.

Step V: Incremental Rollout  

An incremental rollout plan that progressively introduces Java 21 into production should be used to reduce risk. This step-by-step strategy enables you to monitor performance, collect feedback, and fix any developing concerns before full deployment. Controlling the rollout pace reduces the possibility of system-wide outages.

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Step VI: Leverage Support Resources  

During the update, use accessible support resources such as Eclipse Java 21,

Gradle Java 21, community forums, and vendor support channels. These sites can offer insights, troubleshooting advice, and solutions to typical problems seen during upgrades.

Following this approach will provide a seamless transition to Java 21, allowing your business to benefit from the most recent improvements in Java while retaining application stability and security.

Comparison: Java 17 vs. Java 21

Feature	Java 17	Java 21
Release Date	September 2021	September 2023
Support Type	Long-Term Support (LTS)	Long-Term Support (LTS)
Sealed Classes	Introduced	Improved Stability
Pattern Matching for Switch	Preview Feature	Standardized Feature
Virtual Threads	Not Available	Introduced (Project Loom)
String Templates	Not Available	Introduced
Record Patterns	Not Available	Introduced
Sequenced Collections	Not Available	Introduced
Foreign Function & Memory API	Incubator Stage	Enhanced and Stable
Performance	Improved GC and startup times	Advanced concurrency and memory optimizations
Security Updates	Regular patches	Latest security enhancements and patches
Developer Productivity	Moderate improvements	Significant enhancements with new syntactic features
Use Cases	Stable enterprise applications	Modern, high performance, and scalable applications

Java 21: Your Gateway to A Better Future

Java 21 is preferred over Java 17, particularly for enterprises seeking to remain competitive and future-proof their applications. With key advances such as Virtual Threads, Record Patterns, and the Foreign Function & Memory API, Java 21 improves concurrency, developer productivity, and performance optimization. 

While Java 17 is stable and well-suited for corporate applications, Java 21’s improvements transform it into a more powerful tool for contemporary, scalable, and secure application development. Upgrading to Java 21 provides access to the most recent features, long-term support, and a future-ready architecture.

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