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# Java 9 New Features Java 9 was released on September 22, 2017, bringing many new features, the most significant of which is the implemented module system. Next, we will introduce the new features of Java 9 in detail. ## Java 9 New Features * **Module System**: A module is a container for packages. One of the biggest changes in Java 9 is the introduction of the module system (Project Jigsaw). * **REPL (JShell)**: Interactive programming environment. * **HTTP 2 Client**: HTTP/2 is the latest version of the HTTP protocol. The new HttpClient API supports WebSocket and HTTP/2 streams, as well as server push features. * **Improved Javadoc**: Javadoc now supports searching within API documentation. Additionally, Javadoc output now conforms to HTML5 standards. * **Multi-Release JAR Files**: The multi-release JAR feature allows you to create libraries that use different class versions depending on the specific Java version they are run on. * **Collection Factory Methods**: New static factory methods in the List, Set, and Map interfaces allow you to create immutable instances of these collections. * **Private Interface Methods**: You can use private methods in interfaces. We can write private methods in interfaces using the private access modifier. * **Process API**: Improved API for controlling and managing operating system processes. Introduces `java.lang.ProcessHandle` and its nested interface `Info` to help developers avoid the common need to use native code to get a local process's PID. * **Improved Stream API**: The improved Stream API adds some convenience methods, making stream processing easier and allowing you to write complex queries using collectors. * **Improved try-with-resources**: If you already have a resource that is final or effectively final, you can use that variable in a try-with-resources statement without having to declare a new variable in the statement. * **Improved @Deprecated Annotation**: The `@Deprecated` annotation can mark the status of a Java API, indicating that the marked API will be removed or is already broken. * **Improved Diamond Operator**: Anonymous classes can now use the Diamond Operator. * **Improved Optional Class**: `java.util.Optional` has added many new useful methods, and Optional can now be directly converted to a Stream. * **Multi-Resolution Image API**: Defines a multi-resolution image API, making it easy for developers to manipulate and display images of different resolutions. * **Improved CompletableFuture API**: The asynchronous mechanism of the `CompletableFuture` class can execute operations when the `ProcessHandle.onExit` method exits. * **Lightweight JSON API**: A lightweight JSON API is built-in. * **Reactive Streams API**: Java 9 introduces a new Reactive Streams API to support reactive programming in Java 9. For more new features, please refer to the official website: [What's New in JDK 9](https://docs.oracle.com/javase/9/whatsnew/toc.htm) JDK 9 Download: [http://www.oracle.com/technetwork/java/javase/downloads/jdk9-doc-downloads-3850606.html](http://www.oracle.com/technetwork/java/javase/downloads/jdk9-doc-downloads-3850606.html) In the examples for the Java 9 article, we will use the jdk 1.9 environment. You can use the following command to check the current jdk version: $ java -version java version "9-ea"Java(TM) SE Runtime Environment (build 9-ea+163)Java HotSpot(TM) 64-Bit Server VM (build 9-ea+163, mixed mode) Next, we will introduce the new features of Java 9 in detail: | No. | Feature | | --- | --- | | 1 | (#) | | 2 | [REPL (JShell)](#) | | 3 | (#) | | 4 | (#) | | 5 | (#) | | 6 | (#) | | 7 | (#) | | 8 | (#) | | 9 | (#) | | 10 | [@Deprecated](#) | | 11 | (#) | | 12 | (#) | | 13 | (#) | | 14 | (#) |