<<TableOfContents(2)>>

= OpenJDK21 =

== Install from Adoptium ==
 * https://adoptium.net/temurin/releases
 * https://github.com/adoptium/temurin21-binaries/releases/tag/jdk-21.0.7%2B6

{{{#!highlight sh
cd ~
wget https://github.com/adoptium/temurin21-binaries/releases/download/jdk-21.0.7%2B6/OpenJDK21U-jdk_x64_linux_hotspot_21.0.7_6.tar.gz
tar tvzf OpenJDK21U-jdk_x64_linux_hotspot_21.0.7_6.tar.gz 
tar xvzf OpenJDK21U-jdk_x64_linux_hotspot_21.0.7_6.tar.gz 
nano ~/.bashrc
JAVA_HOME=/home/vitor/jdk-21.0.7+6/
MAVEN_HOME=/home/vitor/apache-maven-3.8.6/
PATH=$JAVA_HOME/bin/:$PATH:$MAVEN_HOME/bin/
# reload bashrc
# . ~/bashrc 
}}}

== List of JEPs ==
 * https://openjdk.org/jeps/0

== Records ==
 * https://openjdk.org/jeps/395
Introduced in release 16. 

To model data as data. Easy and concise manner to declare data-carrier classes that by default make their data immutable. Can be described as nominal tuples.

{{{#!highlight java
  record Point(int x, int y) { }
}}}

== Virtual threads ==
 * https://openjdk.org/jeps/444
Virtual threads are lightweight threads that dramatically reduce the effort of writing, maintaining, and observing high-throughput concurrent applications.

{{{#!highlight java 
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    IntStream.range(0, 10_000).forEach(i -> {
        executor.submit(() -> {
            Thread.sleep(Duration.ofSeconds(1));
            return i;
        });
    });
}  // executor.close() is called implicitly, and waits
//---

void handle(Request request, Response response) {
    var url1 = ...
    var url2 = ...
 
    try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
        var future1 = executor.submit(() -> fetchURL(url1));
        var future2 = executor.submit(() -> fetchURL(url2));
        response.send(future1.get() + future2.get());
    } catch (ExecutionException | InterruptedException e) {
        response.fail(e);
    }
}
 
String fetchURL(URL url) throws IOException {
    try (var in = url.openStream()) {
        return new String(in.readAllBytes(), StandardCharsets.UTF_8);
    }
}
}}}

== Compact Source Files and Instance Main Methods ==
 * https://openjdk.org/jeps/512
Evolve the Java programming language so that beginners can write their first programs without needing to understand language features designed for large programs.

{{{#!highlight java
// java HelloWorld.java

void main() {
    IO.println("Hello, World!");
}

//----
void main() {
    String name = IO.readln("Please enter your name: ");
    IO.print("Pleased to meet you, ");
    IO.println(name);
}

//----
void main() {
    var authors = List.of("James", "Bill", "Guy", "Alex", "Dan", "Gavin");
    for (var name : authors) {
        IO.println(name + ": " + name.length());
    }
}

}}}