In this article, we will present the new features of Java 17.
1. Introduction
JDK 17 is a long-term support (LTS) version and was released on September 14, 2021. It has the following new features:
- JEP 415: Context-Specific Deserialization Filters
- JEP 414: Vector API (Second Incubator)
- JEP 412: Foreign Function & Memory API (Incubator)
- JEP 411: Deprecate the Security Manager for Removal
- JEP 410: Remove the Experimental AOT and JIT Compiler
- JEP 409: Sealed Classes
- JEP 407: Remove RMI Activation
- JEP 406: Pattern Matching for switch (Preview)
- JEP 403: Strongly Encapsulate JDK Internals
- JEP 398: Deprecate the Applet API for Removal
- JEP 391: macOS/AArch64 Port
- JEP 382: New macOS Rendering Pipeline
- JEP 356: Enhanced Pseudo-Random Number Generators
- JEP 306: Restore Always-Strict Floating-Point Semantics
In this tutorial, I will demonstrate JEP 406 – Pattern Matching for the switch – via a JShell command.
2. Technologies Used
The example code in this article was built and run using:
- Java 17
- Powershell
- Docker
3. Install JDK17 as a Docker Container
In this step, I will install JDK 17 from the OpenJDK docker image.
3.1 Pull the JDK17
I will pull the latest openjdk image from the docker registry with the following command.
docker pull openjdk
PS C:\MaryZheng\DockerImages> docker pull openjdk Using default tag: latest latest: Pulling from library/openjdk 58c4eaffce77: Pull complete e6a22c806ee8: Pull complete e24190594061: Pull complete Digest: sha256:c841c22e8f9de75a637f9850952ea89a931bdb437af6c2d943ab337cdb299a5e Status: Downloaded newer image for openjdk:latest docker.io/library/openjdk:latest PS C:\MaryZheng\DockerImages>
3.2 Run JDK 17 Docker Container
Enter the following command to start Java 17 and verify with the java version command.
docker run -it openjdk bash
PS C:\MaryZheng\DockerImages> docker run -it openjdk bash bash-4.4# java -version openjdk version "17.0.1" 2021-10-19 OpenJDK Runtime Environment (build 17.0.1+12-39) OpenJDK 64-Bit Server VM (build 17.0.1+12-39, mixed mode, sharing) bash-4.4#
Note: JDK 17.0.1 is installed.
4. Pattern Matching for Switch
I will demonstrate JDK 17 feature – Pattern Matching for switch – via Jshell commands. The switch statement is enhanced to match expressions with multiple patterns. Each pattern has a specific operation, so complex data patterns can be expressed concisely and safely.
4.1 Launch Jshell
Enter the following command to launch Jshell.
bash-4.4# jshell --enable-preview Oct 23, 2021 12:38:51 PM java.util.prefs.FileSystemPreferences$1 run INFO: Created user preferences directory. | Welcome to JShell -- Version 17.0.1 | For an introduction type: /help intro jshell>
4.2 Switch Statement
Enter the following Switch statement which matches four expressions – Integer, Long, Double, and String – in a Jshell prompt.
testSwitch method
String testSwitch(Object o){
String out="NA";
switch (o) {
case Integer i -> out= String.format("int %d", i);
case Long l -> out= String.format("long %d", l);
case Double d -> out= String.format("double %f", d);
case String s -> out= String.format("String %s", s);
default -> out= o.toString();
};
return out;
}The JShell output confirms that the testSwitch method is created.
jshell> String testSwitch(Object o){
...> String out="NA";
...> switch (o) {
...> case Integer i -> out= String.format("int %d", i);
...> case Long l -> out= String.format("long %d", l);
...> case Double d -> out= String.format("double %f", d);
...> case String s -> out= String.format("String %s", s);
...> default -> out= o.toString();
...> };
...> return out;
...> }
| created method testSwitch(Object)
jshell>Verify the testSwitch method with four different object types.
verify testSwitch method
jshell> testSwitch(100)
$2 ==> "int 100"
jshell> testSwitch("Mary Test")
$3 ==> "String Mary Test"
jshell> testSwitch(11.11)
$4 ==> "double 11.110000"
jshell> testSwitch(100000l)
$5 ==> "long 100000"
jshell>As you see here, different object types follow the same logic.
5. Summary
In this article, we demonstrated one of the JDK17 features – switch pattern matching – via the JShell command in a docker container. You can learn more about JDK 17 features here.
6. Download the Source Code
You can download the full source code of this example here: Java 17 New Features Tutorial
