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Exploring Java 21: A Look at the Exciting API Changes

Java, one of the most popular and enduring programming languages, continues evolving with each release. The release of Java 21 brings exciting API changes that enhance the language's capabilities and provide developers with new tools and features to build robust and efficient applications. In this article, we'll explore some key API changes introduced in Java 21.

Pattern Matching for instanceof

One of the most anticipated features in Java 21 is the enhancement of pattern matching for the instanceof operator. This feature simplifies the common pattern of casting objects after checking their type. In previous versions, you would typically write code like this:

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With Java 21, you can streamline this code using pattern matching:

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This change not only reduces boilerplate code but also makes the code more readable and less error-prone.

Records Improvements

Records, introduced in Java 16, have become a popular feature for defining classes that are primarily containers for data. In Java 21, records receive enhancements to make them even more powerful and flexible.

Record Components Without Accessors: In previous versions, record components were required to have accessors (getters). In Java 21, you can declare a record component without an accessor method, making it a non-final field. This allows you to provide custom behavior for that field.

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Custom Constructors: Java 21 allows you to declare constructors in records. This lets you create records with additional constructors, providing more flexibility when initializing record instances.

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Enhanced Enums

Enums in Java 21 also receive some improvements to increase their flexibility and utility.

Sealed Enums: You can now apply the sealed modifier to enums. Sealed enums restrict which subclasses can extend them, providing better control over the hierarchy.

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Text Blocks in Enums: Enums can now contain text blocks, allowing you to store multiline descriptions or templates directly in enum constants.

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Deprecating and Removing APIs

In every Java release, some APIs are deprecated or removed to clean up the language and encourage the adoption of more modern alternatives. Developers should consider these changes to ensure their codebase remains up-to-date and maintainable.

In Java 21, certain APIs have been deprecated or removed, such as the SecurityManager and related classes. Developers are encouraged to migrate to the more secure and efficient alternatives.


Java 21 introduces several exciting API changes that enhance the language's capabilities and make it even more developer-friendly. The improvements to pattern matching, records, and enums simplify code, increase expressiveness, and reduce boilerplate. Additionally, deprecating and removing outdated APIs ensures that Java remains a secure and reliable platform for building software.

As with any new release, Java developers need to stay informed about these changes and consider how they can leverage them to improve their codebase. Java 21 demonstrates the language's commitment to innovation and its dedication to providing developers with the tools they need to create robust and efficient applications.

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