New features in Java 18

Java language feature series

• New features of Java5
• New features of Java6
• New features of Java7
• New features of Java8
• New features of Java9
• What's new in Java 10
• What's new in Java 11
• New features in Java 12
• New features in Java 13
• New features in Java 14
• New features in Java 15
• New features in Java 16
• New features in Java 17
• New features in Java 18
• New features in Java 19
• New features of Java 20

sequence

This article mainly describes the new features of Java 18

version number

 java -version
openjdk version "18" 2022-03-22
OpenJDK Runtime Environment (build 18+36-2087)
OpenJDK 64-Bit Server VM (build 18+36-2087, mixed mode, sharing)

It can be seen from the version information that it is build 18+36

Feature list

JEP 400: UTF-8 by Default

Before java18, Charset.defaultCharset() was determined according to the operating system, user locale, etc., resulting in different default charsets for different operating systems. This time, it was changed to UTF-8.
To unify java18 into UTF-8, you need -Dfile.encoding=UTF-8 to set it. If you want to continue to use the previous judgment method, you can set it through -Dfile.encoding=COMPAT

JEP 408: Simple Web Server

Provides an out-of-the-box HTTP file server like Python's SimpleHTTPServer ( python -m SimpleHTTPServer [port] ) that can be started via jwebserver -p 9000

 jwebserver -p 9000
Binding to loopback by default. For all interfaces use "-b 0.0.0.0" or "-b ::".
Serving /tmp and subdirectories on 127.0.0.1 port 9000
URL http://127.0.0.1:9000/

It can also be customized and started in the code

 jshell> var server = SimpleFileServer.createFileServer(new InetSocketAddress(8080),
   ...> Path.of("/some/path"), OutputLevel.VERBOSE);
jshell> server.start()

JEP 413: Code Snippets in Java API Documentation

In the past, to show code through javadoc, you can use @code as follows

 <pre>{@code
    lines of source code
}</pre>

But its disadvantage is that it has to be wrapped with pre, resulting in that the fragment cannot contain html tags, and the indentation is not very flexible

This time, the @snippet tag is introduced to javaDoc, so there is no need to escape the html tag.

 /**
 * The following code shows how to use {@code Optional.isPresent}:
 * {@snippet :
 * if (v.isPresent()) {
 *     System.out.println("v: " + v.get());
 * }
 * }
 */

You can also directly refer to the source code to avoid the disconnection between the javadoc code and the actual code

 /**
 * The following code shows how to use {@code Optional.isPresent}:
 * {@snippet file="ShowOptional.java" region="example"}
 */

JEP 416: Reimplement Core Reflection with Method Handles

Reimplement java.lang.reflect.Method, Constructor and Field through Method Handles to replace the implementation of Method::invoke, Constructor::newInstance, Field::get, and Field::set generated by bytecode to support Project Valhalla, Reduce expansion costs for future

JEP 417: Vector API (Third Incubator)

JDK16 introduced JEP 338: Vector API (Incubator) provides jdk.incubator.vector for vector computation
JDK17 improves and serves as the second round of incubator JEP 414: Vector API (Second Incubator)
JDK18 improves and acts as a third round incubator

JEP 418: Internet-Address Resolution SPI

Provides SPI for parsing network addresses, namely the InetAddressResolverProvider of the java.net.spi package
It is convenient to prepare for project loom (currently, the API of InetAddress will block the system call), and it is also convenient for customization and testing

JEP 419: Foreign Function & Memory API (Second Incubator)

JEP 370: Foreign-Memory Access API (Incubator) of JDK14 introduces the Foreign-Memory Access API as an incubator
JDK15's JEP 383: Foreign-Memory Access API (Second Incubator) Foreign-Memory Access API as a second-round incubator
JDK16's JEP 393: Foreign-Memory Access API (Third Incubator) as the third round, it introduces the Foreign Linker API
JDK17 introduces JEP 412: Foreign Function & Memory API (Incubator) as the first round of incubator
JDK18 is used as the second round of incubator

JEP 420: Pattern Matching for switch (Second Preview)

The pattern matching of instanceof is used as a preview in JDK14, as a second-round preview in JDK15, and positive in JDK16

 static String formatterPatternSwitch(Object o) {
    return switch (o) {
        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        -> o.toString();
    };
}

JDK17 introduces JEP 406: Pattern Matching for switch (Preview)
JDK18 is used as a preview of the second round

JEP 421: Deprecate Finalization for Removal

Abandon the finalize method to facilitate subsequent removal

Detailed Interpretation

Listed above are major features, in addition to some api updates and discards, mainly see JDK 18 Release Notes , here are a few examples.

Add item

• SerialGC, ParallelGC, ZGC support String Deduplication

  Available -XX:+UseStringDeduplication Open

• Map from an Element to its JavaFileObject

  Added Elements.getFileObjectOf(Element) to map to JavaFileObject

• Configurable Card Table Card Size JDK-8272773

  You can use -XX:GCCardSizeInBytes to set the card table size

• Allow G1 Heap Regions up to 512MB JDK-8275056

  The maximum allowed heap regions for G1 is from the previous 32MB to 512MB

• JDK Flight Recorder Event for Finalization JDK-8266936

  Added jdk.FinalizerStatistics

remove item

• Removal of Google's GlobalSign Root Certificate JDK-8225083

  Removed google's GlobalSign root certificate

• Removal of Empty finalize() Methods in java.desktop Module JDK-8273102

  Remove the empty finalize() method in the java.desktop module

• Removal of impl.prefix JDK System Property Usage From InetAddress JDK-8274227

  Remove the impl.prefix property and use the spi of InetAddressResolver instead

• Removal of Support for Pre JDK 1.4 DatagramSocketImpl Implementations JDK-8260428

  Remove DatagramSocketImpl before jdk1.4

• Removal of Legacy PlainSocketImpl and PlainDatagramSocketImpl Implementations JDK-8253119

  Removed the old implementations of java.net.SocketImpl and java.net.DatagramSocketImpl PlainSocketImpl, PlainDatagramSocketImpl
  jdk.net.usePlainDatagramSocketImpl attributes are also removed

obsolete

See deprecated-list for the full list

• Deprecated Subject::doAs for Removal JDK-8267108

  javax.security.auth.Subject::doAs Prepare for removal

• Deprecated sun.misc.Unsafe Methods That Return Offsets JDK-8277863

  objectFieldOffset, staticFieldOffset, staticFieldBase methods in sun.misc.Unsafe are abandoned

• Terminally Deprecated Thread.stop JDK-8277861

  Deprecated Thread.stop in preparation for subsequent removal

• Obsoleted Product Options -XX:G1RSetRegionEntries and -XX:G1RSetSparseRegionEntries JDK-8017163

  Obsolete -XX:G1RSetRegionEntries and -XX:G1RSetSparseRegionEntries

Known Issues

• Extended Delay Before JDK Executable Installer Starts From Network Drive JDK-8274002

  On Windows 11 and Windows Server 2022, the extraction of temporary installation files may be somewhat slow when booting from a mapped network drive. The installer will still work, but there may be a temporary delay.

summary

Java18 mainly has the following features

• JEP 400: UTF-8 by Default
• JEP 408: Simple Web Server
• JEP 413: Code Snippets in Java API Documentation
• JEP 416: Reimplement Core Reflection with Method Handles
• JEP 417: Vector API (Third Incubator)
• JEP 418: Internet-Address Resolution SPI
• JEP 419: Foreign Function & Memory API (Second Incubator)
• JEP 420: Pattern Matching for switch (Second Preview)
• JEP 421: Deprecate Finalization for Removal

doc

• JDK 18 Features
• JDK 18 Release Notes
• Consolidated JDK 18 Release Notes
• Java SE 18 deprecated-list
• The Arrival of Java 18
• JDK 18 G1/Parallel/Serial GC changes