Overview of Java >= 9

Written by: Abdul Habra
Last Update: 2020.08.26

Overview of features add to Java 9 and higher. This reflects the author's opinion :)

3 Laws Of Meeting

1. Law of Two Feet: Walk away if you are not learning
2. Law of Big Mouth: Ask questions anytime
3. Law of Equal Participation (a.k.a Uniform Distribution): Do not take over the talk

SdkMan

Tool to manage parallel versions of SDKs (Java and others). Same idea as jEnv, but better :)

Useful commands:

• sdk help
• sdk list java # List all available verions
• sdk current java # Show what's currently in use
• sdk install java 8.0.202-zulu
• sdk install java 13.0.2-zulu
• sdk use java 13.0.2-zulu # For current session of shell
• sdk default java 13.0.2-zulu # Subsequent shells will use
• sdk uninstall java 13.0.2-zulu

Java Versions

Version	Version Scheme	Release	Oracle Support
8	1.8.0_202	2014/3	12/2020
9	9.x.y	2017/9	to next
10	10.x.y	2018/3	to next
11	11.x.y	2018/9	9/2023 LTS
12	12.x.y	2019/3	to next
13	13.x.y	2019/9	to next
14	14.x.y	2020/3	to next
15	15.x.y	2020/9	to next

• LTS: Long-Term-Support starting with 11
• LTS every 3 years
• Non-LTS every 6 months
• Version scheme is NOT semantic versioning: $FEATURE.$INTERIM.$UPDATE.$PATCH

Interesting Features

This is a selection based on the author's views 😃

Improved Java Docs - Java 9

Include search box: https://docs.oracle.com/javase/9/docs/api/index.html?overview-summary.html

Jshell - Java 9

• REPL: Read Evaluate Print Loop

/help
/exit
int a=42
System.out.println(a)

Use tab key for auto-colmplete

JCMD Utility - Java 9

Sends diagnostic command requests to a running Java Virtual Machine (JVM).

• jcmd : List running VMs and their PIDs
• jcmd PID help : help for selected PID
• jcmd PID GC.class_histogram : List classes for given PID

Run Java File - Java 11

Suppose we have this class:

public class Hello{
    public static void main(String[] args){
        System.out.println("Hello 42");
    }
}

You can:

java Hello.java

No need for running javac

• You can have multiple classes in a single file

Java Shebang Files - Java 11

Create a file named for example shebang

#!/path/to/bin/java --source 11

public class Foo {
    public static void main(String[] args) {
        System.out.println("Java Says: Hello " + System.getProperty("user.name"));
    }
}

Remember to chmod +x shebang

Collections Factory Methods - Java 9

List<Integer> list = List.of(1, 2);
Set<Integer> set = Set.of(1, 2); // elements must be unique
Map<Integer, String> map1 = Map.of(1, "a", 2, "b");
Map<Integer, String> map2 = Map.ofEntries(Map.entry(1, "a"), Map.entry(2, "b"));
Map.Entry<Integer, String> entry = Map.entry(1, "a");

Interface Private Methods - Java 9

Local Var Type Inference - Java 10

var x = "a";
System.out.println(x.getClass());

Will print: class java.lang.String

• The var must be initialized to a non-null value, and must be local.

Switch Expressions - Java 12 Preview, 14 Standard

This is a preview feature. Use --enable-preview at command line to enable.

int daysInMonth = switch(month) {
    case 2 -> 28;
    case 1, 3, 5, 7, 8, 10, 12 -> 31;
    case 4, 6, 9, 11 -> 30;
    default -> throw new IllegalArgumentException("Invalid value of month: " + month);
};

Text Blocks - Java 13 Preview

Use --enable-preview at command line to enable.

• Multiline string inside a triple-double quotes:

String html = """
<div>
  This is java's Multiline text block
</div>
""";

Records - Java 14 Preview

Similar to Scala's Case Class.

// java 14
record Book(String title, String author) {}

Is equivilant to

// pre java 14
final class Book {
    public final String title;
    public final String author;

    public Book(String title, String author) {
        this.title = title;
        this.author = author;
    }

    // Plus equals, hashCode, toString
}

Finally, no need to Lombok or get/set code generators.

Reactive Streams - Java 9

Concurrent, distributed, asynchronous, unbounded, reactive streams.

• java.util.concurrent.Flow: Has the following static inner interfaces

  • Subscriber: Informs Publisher that it can accept N number of items
  • Publisher: If it has items, will push max of N items to Subscriber
  • Processor: Both Publisher and Subscriber
  • Subscription: Binds a single publisher with a single subscriber

• This process prevents overloading of subscriber. It is called backpressure

• Relationship from Publisher to Subscriber is 1-to-N

• During subscription, Publisher passes a Subscription object to Subscriber

HTTP Client - Incubated in Java 9, standardized in Java 11

• Support http/1.1 and 2. Supports WebSockets
• java.net.http.Http
• Uses fluent API

import java.net.http.*;
import java.net.http.HttpResponse.BodyHandlers;

HttpRequest request = HttpRequest.newBuilder()
      .uri(URI.create("http://example.com/")).build();

HttpClient client = HttpClient.newHttpClient();
client.sendAsync(request, BodyHandlers.ofString())
      .thenApply(HttpResponse::body)
      .thenAccept(System.out::println)
      .join();

Will print content of page.

Module System / Jigsaw Project - Java 9

• Control JDK modules
• Somewhat similar to OSGi
• imho: Revenge of the EJB architects.

Epsilon Garbage Collector - Java 11

• Allocates memory on heap, but no reclamaion.
• Experimental
• Useful for performance testing

Depracations

• Applet API - Java 9
• Nashorn JS Engine - Java 11

Removals

• Java EE and CORBA Modules - Java 11
  • java.xml.ws
  • java.xml.bind
  • java.activation
  • java.xml.ws.annotation
  • java.corba
  • java.transaction
  • java.se.ee
  • jdk.xml.ws
  • jdk.xml.bind
• Thread.destroy() and Thread.stop(Throwable) - Java 11
• Java Plugin and Java WebStart - Java 11
• JavaFX - Java 11

References

1. https://www.oracle.com/technetwork/java/java-se-support-roadmap.html
2. https://www.baeldung.com/java-time-based-releases
3. https://www.baeldung.com/new-java-9
4. https://www.baeldung.com/java-10-overview
5. https://www.baeldung.com/java-9-http-client
6. https://www.baeldung.com/java-single-file-source-code
7. https://dzone.com/articles/39-new-features-and-apis-in-jdk-12
8. https://dzone.com/articles/reactive-streams-in-java-9