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This article introduces the relevant knowledge of "What are the new features of Java15". In the operation process of actual cases, many people will encounter such difficulties. Next, let Xiaobian lead you to learn how to deal with these situations! I hope you can read carefully and learn something!

new features

JDK 15 New Features List:

IDJEPFeature1339Edwards-Curve Digital Signature Algorithm (EdDSA)2360Sealed Classes (Preview)3371Hidden Classes4372Remove the Nashorn JavaScript Engine5373Reimplement the Legacy DatagramSocket API6374Disable and Deprecate Biased Locking7375Pattern Matching for instanceof (Second Preview)8377ZGC: A Scalable Low-Latency Garbage Collector9378Text Blocks10379Shenandoah: A Low-Pause-Time Garbage Collector11381Remove the Solaris and SPARC Ports12383Foreign-Memory Access API (Second Incubator)13384Records (Second Preview)14385Deprecate RMI Activation for Removal

JDK 15 released 14 new features at once. The stack length below takes everyone to interpret these new features!

339:Edwards-Curve Digital Signature Algorithm (EdDSA)

Edwards-Curve Digital Signature Algorithm (EdDSA), a cryptographic signature algorithm based on the Edwards-Curve Digital Signature Algorithm (EdDSA) described in RFC 8032, implements a RFC 8032 standardized scheme, but it cannot replace ECDSA.

EdDSA is a modern elliptic curve signature scheme that has many advantages over existing signature schemes in JDK.

360:Sealed Classes (Preview)

Enclosed classes (preview features), which can be closed classes and/or closed interfaces, are used to enhance the Java programming language and prevent other classes or interfaces from extending or implementing them.

This is awesome. With this feature, it means that in the future, you don't have to inherit it if you want to inherit it, but you have to get permission.

Consider this example:

public abstract sealed class Student permits ZhangSan, LiSi, ZhaoLiu { ... }

The class Student is sealed, indicating that it is a closed class and only allows the specified 3 subclasses to inherit.

371:Hidden Classes

Hidden classes, which is also an interesting feature at first glance.

Hidden classes are designed for frameworks, and hidden classes cannot be used directly by the bytecode of other classes, but can only be generated at runtime and used indirectly through reflection.

372:Remove the Nashorn JavaScript Engine

Removed Nashorn JavaScript scripting engine, APIs, and jjs tools. These were marked as deprecated as early as JDK 11, and JDK 15 was removed as normal.

Nashorn is a JavaScript scripting engine introduced in JDK 1.8 to replace the Rhino scripting engine. Nashorn is a complete implementation of ECMAScript-262 5.1, which enhances Java and JavaScript compatibility and greatly improves performance.

Why remove?

The official description is that with the structure of ECMAScript scripting language, API adaptation speed is getting faster and faster, maintaining Nashorn is too challenging, so…

373:Reimplement the Legacy DatagramSocket API

Reimplemented the old DatagramSocket API interface, changed java. net.DatagramSocket and java. net.MulticastSocket to a simpler, more modern implementation, easier to maintain and debug.

The new underlying implementation, which will make it easy to use virtual threads, is currently being explored in the Loom project. This is also a follow-on update to JEP 353, which has reimplemented the Socket API.

374:Disable and Deprecate Biased Locking

Prepare to disable and abolish bias locks, which are disabled by default in JDK 15 and all related command line options are deprecated.

It will be decided later whether or not to continue supporting biased locks, since the cost of maintaining synchronization optimizations for such locks is too high.

375:Pattern Matching for instanceof (Second Preview)

Pattern matching (second preview). The first preview was presented in JDK 14. Click here to see a detailed tutorial written before the stack length.

Before Java 14:

if (object instanceof Kid) { Kid kid = (Kid) object; // ...} else if (object instanceof Kiddle) { Kid kid = (Kid) object; // ...}

Java 14+：

if (object instanceof Kid kid) { // ...} else if (object instanceof Kiddle kiddle) { // ...}

Java 15 doesn't tweak this feature, it continues to preview features, just to gather more user feedback, probably premature.

377:ZGC: A Scalable Low-Latency Garbage Collector

ZGC: A scalable, low-latency garbage collector.

ZGC was first integrated in JDK 11, JDK 15 just changed the ZGC garbage collector from a preview feature to a formal feature, yes, it turned positive.

This JEP does not change the default GC, which remains G1.

378:Text Blocks

A text block is a multiline string that avoids most escape symbols, automatically formats strings in predictable ways, and gives developers control over formatting when needed.

Text blocks were originally added in JDK 12, but were eventually undone, then added as preview features in JDK 13, then previewed again in JDK 14, and finally turned positive in JDK 15, with no further changes.

Take a look at this example and you will understand:

Before Java 13:

String html = "\n" + " \n" + "

Hi, Java Technology Stack

\n" + "

Welcome to share more dry goods

\n" + " \n" + "\n";

Java 13+：

String html = """

Hi, Java Technology Stack

Welcome to share more dry goods

""";

Get rid of those useless newlines and splices, isn't it too cool. This detailed tutorial plans to publish another article, paying attention to the public Java technology stack for the first time.

379:Shenandoah: A Low-Pause-Time Garbage Collector

Shenandoah: A garbage collector with low dwell time.

Shenandoah was first integrated in JDK 12, JDK 15 just changed Shenandoah garbage collector from preview feature to official feature, yes, it is positive again.

381:Remove the Solaris and SPARC Ports

Solaris and SPARC ports removed.

Removed source code and build support for Solaris/SPARC, Solaris/x64, and Linux/SPARC ports. These ports were already marked as deprecated in JDK 14, and it is not surprising that JDK 15 was removed.

383:Foreign-Memory Access API (Second Incubator)

External memory access API (secondary incubation) allows Java applications to safely and efficiently access external memory outside the Java heap.

This was originally an incubation feature in JDK 14, and JDK 15 continues to incubate a second time with some updates to its API.

384:Records (Second Preview)

Records was first introduced as a preview feature in JDK 14, and JDK 15 continues with a second preview.

Records can kill Lombok in some cases, automatically generating class constructors, toString(), hashCode(), equals(), and getter-like variable access methods.

Usage:

public record Student(String name, int id, int age) {}

Actual generation:

Does it feel like Lombok? You can click here to see the detailed tutorial written before the stack length.

385:Deprecate RMI Activation for Removal

Deactivate RMI activation for future deletion.

To be clear, RMI activation is an obsolete component of RMI that has been optional since Java 8.

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