Deep Dive Java 17 Devoxx UK

Java 17: Deep Dive
José Paumard
Java Developer Advocate
Java Platform Group

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https://www.pluralsight.com/authors/jose-paumard
https://dev.java

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
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Dev.java
Java 8 Java 11

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Java 17 – LTS !
Java 8 Java 11

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OpenJDK?
https://openjdk.java.net

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New Release Cadence!
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http://jdk.java.net/

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http://jdk.java.net/
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2018 2019 2020 2021 2022 2023 2024 2025

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https://www.oracle.com/java/
technologies/javase-
downloads.html
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2018 2019 2020 2021 2022 2023 2024 2025

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New New Release Cadence!
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1) LTS: 3 years  2 years
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https://mreinhold.org/blog/forward-even-faster
https://blogs.oracle.com/java/post/
moving-the-jdk-to-a-two-year-lts-cadence

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https://mreinhold.org/blog/forward-even-faster
moving-the-jdk-to-a-two-year-lts-cadence

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2) Free licence (dev + prod)
3) No click-through
free-java-license

Sept.
2021
Mars
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Mars
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Years
JDK 8 LTS JDK 9-11 JDK 12-17
JDK 9
JDK 10
JDK 11 LTS
JDK 12
JDK 13
JDK 14
JDK 15
JDK 16
JDK 17 LTS
Features
From 8 to 17
Copyright © 2021, Oracle and/or its affiliates
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Language
Type inference for locals (var)
Switch expressions
Text blocks
Record classes
Sealed classes
Pattern matching for instanceof
JDK 17: New Features Since the JDK 8
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Tools
jshell
jlink
jdeps
jpackage
java source code launcher
javadoc search + API history
JVM
Garbage Collectors: G1, ZGC
AArch64 support: Windows, Mac, Linux
Docker awareness
Class Data Sharing by default
Helpful NullPointerExceptions
Hidden classes
Libraries
HTTP client
Collection factories
Unix-domain sockets
Stack walker
Deserialization filtering
Pseudo-RNG, SHA-3, TLS 1.3

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Copyright © 2021, Oracle and/or its affiliates | Confidential: Internal/Restricted/Highly Restricted
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Tools

Language
Switch expressions
Text blocks
Record classes
Sealed classes
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Tools
jshell
jlink
jdeps
jpackage
JVM
Docker awareness
Hidden classes
Libraries
HTTP client
Unix-domain sockets
Stack walker
Tools
jshell
jlink
jdeps
jpackage

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Step 1: Hello World
Launching Single File Source Code
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
$ java HelloWorld.java

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Step 2: Add 3rd party dependencies
System.out.println(RandomUtils.nextInt());
}
}
$ java -cp /path/to/commons-lang3-3.12.0.jar HelloWorld.java

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Step 3: Execute a shebang file
#!/path/to/your/bin/java --source 17
System.out.println("Hello World!");
}
}
$ ./HelloWorld

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Create a runtime image
JLink: Creating Custom Runtime Images
$ jlink
--module-path mods
--add-modules org.mycompany.mymodule
--output myapp-image

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Create a runtime image with a launcher
# create the image
$ jlink
--module-path mods
--add-modules com.example.main
--launcher app=com.example.app/com.example.app.Main
--output app-image
# launch
$ app-image/bin/app

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The smallest runtime image
$ jlink
--add-modules java.base
--output jdk.base
$ du –sh jdk.base jdk-17
40M jdk.base
288M jdk-17

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Supported Installers: MSI, EXE, RPM, DEB, PKG, DMG
JPackage: Creating Custom Installers
$ jpackage
--name my-installer
--app-version 1.0
--win-dir-chooser --win-console --win-shortcut
--module-path mymodules/my-app-1.0.jar
--module org.myapp/org.mycompany.myapp.MainClass

11/2/2021
Copyright © 2021, Oracle and/or its affiliates | Confidential: Internal/Restricted/Highly Restricted
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API

Language
Switch expressions
Text blocks
Record classes
Sealed classes
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Tools
jshell
jlink
jdeps
jpackage
JVM
Docker awareness
Hidden classes
Libraries
HTTP client
Unix-domain sockets
Stack walker
Libraries
HTTP client
Unix-domain sockets
Stack walker

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Step 1: create a request
HttpClient API
HttpRequest request =
HttpRequest.newBuilder()
.uri(URI.create("https://example.com"))
.header("Accept-Encoding", "gzip")
.header("Accept", "text/xml")
.GET()
.build();

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Step 2: create a client
HttpClient API
HttpClient client =
HttpClient.newBuilder()
.version(HttpClient.Version.HTTP_1_1)
.connectTimeout(Duration.ofSeconds(20))
.build();

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Step 3: send the request
HttpClient API
HttpResponse<InputStream> response =
client.send(request,
HttpResponse.BodyHandlers.ofInputStream());
InputStream inputStream = response.body();

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Step 3: send the request
HttpClient API
HttpResponse<Stream<String>> response =
client.send(request,
HttpResponse.BodyHandlers.ofLines());
Stream<String> lines = response.body();

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Open a web server for serving a single directory hierarchy.
Options:
Simple HttpServer: Command Line Tool & API
$ java -m jdk.httpserver
-b, --bind-address - Address to bind to. Default: 127.0.0.1 or ::1
(loopback).
For all interfaces use "-b 0.0.0.0" or "-b ::".
-d, --directory - Directory to serve. Default: current directory.
-o, --output - Output format. none|info|verbose. Default: info.
-p, --port - Port to listen on. Default: 8000.

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The API version, in JShell
Supports HTTP only, request handling can be customized
Simple HttpServer: Command Line Tool & API
jshell> var server = SimpleFileServer.createFileServer(
> new InetSocketAddress(8080),
> Path.of("/some/path"),
> OutputLevel.VERBOSE);
jshell> server.start()

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Supported on Linux, MacOS and some flavors of Windows
Both on the server and the client
Unix Domain Sockets
Path home = Path.of("/tmp");
Path file = home.resolve("user.socket");
UnixDomainSocketAddress socketAddress =
UnixDomainSocketAddress.of(file);

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On the server:
On the client:
Unix Domain Sockets
ServerSocketChannel channel =
ServerSocketChannel.open(StandardProtocolFamily.UNIX);
SocketChannel socketChannel = channel.bind(socketAddress).accept();
SocketChannel socketChannel =
SocketChannel.open(socketAddress);

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Current status: getting the execution stack is costly, it captures
the entire stack (getStackTrace() on Thread and Throwable)
Sometimes you only need the first elements of the stack
Idea: have a way of lazily explore the stack, based on a
Stream<StackFrame> and a callback
Stack Frame Walker

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Stack Frame Walker
StackWalker walker =
StackWalker.getInstance(
StackWalker.Option.RETAIN_CLASS_REFERENCE);
walker.forEach(
stackFrame -> System.out.println(stackFrame.getClassName()));

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Stack Frame Walker
Set<String> classNames = ...;
Optional<String> className = walker.walk(
stackFrameStream -> stackFrameStream
.map(StackWalker.StackFrame::getClassName)
.filter(classNames::contains)
.findFirst()
);

Language
Switch expressions
Text blocks
Record classes
Sealed classes
37
Tools
jshell
jlink
jdeps
jpackage
JVM
Docker awareness
Hidden classes
Libraries
HTTP client
Unix-domain sockets
Stack walker
Language
Switch expressions
Text blocks
Record classes
Sealed classes

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Do not override finalize()
Stop doing that!
@Deprecated(since="9")
protected void finalize() throws Throwable {
}

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Do not call new Integer(...)
Stop doing that!
@Deprecated(since="9", forRemoval = true)
public Integer(int value) {
this.value = value;
}
@IntrinsicCandidate
public static Integer valueOf(int i) {
// some code
return new Integer(i);
}

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☕ Coffee Break!

Record and Array Pattern Matching
Record
Sealed Classes
Switch Expression
Constant Dynamic
Inner Classes
private in VM
Nestmates
Pattern Matching for instanceof
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17 Switch on Patterns
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In reference to the Amber by Roger
Zelazny
Project Amber

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A pattern is a combination of a match predicate
that determines if the pattern matches a target,
along with a set of pattern variables
that are conditionally extracted if the pattern
matches the target.
Java 16 : Pattern Match for IntanceOf
Pattern Matching for Java
Gavin Bierman and Brian Goetz, September 2018
https://github.com/openjdk/amber-docs/blob/master/site/design-notes/pattern-matching-for-java.md

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String name = type pattern
String = le nom du pattern
name = binding variable
o = target operand
Type Pattern
if (o instanceof String name) {
// some code
}

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Un Record is built on components
It has a canonical constructor
It is immutable, it cannot extend any class, it is final
It has accessors, equals(), hashCode(), toString()
Record (JDK 16)
public record Car(Color color) {}
public record Rectangle(int width, int height) {}

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Record Deconstruction
if (o instanceof Rectangle rectangle) {
int width = rectangle.width();
int height = rectangle.height();
// do something with width and height
}

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Un record pourra être « déconstruit »
width et height deviennent des binding variables
Record Deconstruction
if (o instanceof Rectangle(int width, int height)) {
}

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Three type patterns
Three pattern binding variables
One target operand
Patterns Matching for Switch
String formatted =
switch(number) {
case Integer i -> String.format("int %d", i);
case Long l -> String.format("long %d", l);
case Double d -> String.format("double %d", d);
}

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Deconstruction + Pattern Matching for Switch
record Square(int edge) {}
record Circle(int radius) {}
double area = switch(shape) {
case Square(int edge) -> edge* edge;
case Circle(int radius) -> Math.PI*radius*radius;
default -> ...;
}

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Sealed Classes (JDK 17)
sealed interface Shape
permits Rectangle, Square, Circle {
}
public final class Rectangle implements Shape {}
public record Circle(Point center) implements Shape {}
public non-sealed abstract class MoreShapes
implements Shape {}

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The hierarchy is « sealed »
Sealed Classes (JDK 17)
sealed interface Shape
permits Rectangle, Square, Circle {
}
public final class Rectangle implements Shape {}
public record Circle(Point center) implements Shape {}
public final class Square implements Shape {}

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The default case becomes useless = total switch
Pattern Matching for Switch + Sealed Types
// default -> ...;
}

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Record Deconstruction (Again)
if (o instanceof Rectangle rectangle) {
int width = rectangle.width();
int height = rectangle.height();
}

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A record can be « deconstructed »
width et height become binding variables
Record Deconstruction (Again)
if (o instanceof Rectangle(int width, int height)) {
}

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Array Pattern Matching
if (o instanceof String[] array && array.length() >= 2) {
// do something with array[0] and array[1]
}

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if (o instanceof String[] {String s1, String s2}) {
// do something with s1 and s2
}

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if (o instanceof Circle[] {Circle(var r1), Circle(var r3)}) {
// do something with r1 and r2
}

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Record Pattern Matching for Switch
record Square(int edge) {}
record Circle(int radius) {}
default -> ...;
}

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You can use var in patterns
Syntaxic Sugars
if (shape instanceof Circle(var center, var radius)) {
// center and radius are binding variables
}
record Point(int x, int y) {}
record Circle(Point center, int radius) implements Shape {}

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You can tell that you do not need a binding variable
Syntaxic Sugars
if (shape instanceof Circle(var center, _)) {
}

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You can nest patterns (nested patterns)
Syntaxic Sugars
if (shape instanceof Circle(var center, _) &&
center instanceof Point(int x, int y)) {
}
if (shape instanceof Circle(Point(int x, int y), _)) {
}

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The deconstruction uses the canonical constructor of a record
What about:
- factory methods?
- classes that are not records?
Deconstruction

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Deconstruction Using Factory Methods
interface Shape {
static Circle circle(double radius) {
return new Circle(radius);
}
static Square square(double edge) {
return new Square(edge);
}
}
record Circle(double radius) {}
record Square(double edge) {}

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Then this code becomes possible:
Deconstruction Using Factory Methods
case Shape.circle(double radius) -> Math.PI*radius*radius;
case Shape.square(double edge) -> edge*edge;
}

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What About Your POJOs?
public class Point {
private int x, y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
public deconstructor(int x, int y) {
x = this.x;
y = this.y;
}
}
Binding variables
They are the same!
external state description
Defensive copy
Overloading?
Overloading!

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You saw patterns with instanceof and switch
Let us see match !
Pattern with Match
Circle circle = ...;
match Circle(var center, var radius) = circle;

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If shape is in fact a rectangle…
You can throw an exception
Pattern with Match
Shape shape = ...;
match Circle(var center, var radius) = shape
else
throw new IllegalStateException("Not a circle");

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If shape is in fact a rectangle …
Or define default values
Pattern with Match
Shape shape = ...;
match Circle(Point center, int radius) = shape
else {
center = new Point(0, 0); // this is called
radius = 1d; // an anonymous matcher
}

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You can use match with more than one pattern…
… or use nested patterns
Pattern with Match
Shape shape = ...;
match Rectangle(var p1, var p2) = shape,
Point(var x0, var y0) = p1,
Point(var x1, var y2) = p2;

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You can create maps with factory methods
This is an extended form of Pattern Matching where you check
the value of a binding variable
More Examples
if (map instanceof Map.withMapping("name", var name) &&
map instanceof Map.withMapping("email", var email)) {
// name and email are binding variables
}

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Pattern combination
More Examples
if (map instanceof Map.withMapping("name", var name) __AND
map instanceof Map.withMapping("email", var email)) {
// name and email are binding variables
}
__AND = pattern combination

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More Examples
{
"firstName": "John",
"lastName": "Smith",
"age": 25,
"address" : {
"street": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": "10021"
}
}
if (json instanceof
stringKey("firstName", var firstName) __AND
stringKey("lastName", var lastName) __AND
intKey("age", var age) __AND
objectKey("address",
stringKey("stree", var street) __AND
stringKey("city", var city) __AND
stringKey("state", var state)
)) {
// firstName, lastName, age,
// street, city, state, ...
// are binding variables
}

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If Java Embraces « Map Literals »
Map<String, String> map = {
"firstName": "John",
"lastName": "Smith",
"age": "25"
}
if (map instanceof
{
"firstName": var firstName,
"lastName": var lastName,
"age": Integer.toString(var age)
}) {
// firstName, lastName, age
// are binding variables
}

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• Constant Patterns: checks the operand with a constant value
• Type Patterns: checks if the operand has the right type, casts
it, and creates a binding variable
Patterns at a Glance

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• Patterns + Deconstruction: checks the operand type, casts it,
bind the component to binding variables
• Patterns + Method: uses a factory method or a deconstructor
• Patterns + Var: infers the right type, and creates the binding
variable
• Pattern + _: infers the right type, but does not create the
binding variable

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« We don’t want to be the first to
include a feature, because every
feature we add will never be
removed »
Brian Goetz,
Java Language Architect
Everything Takes Time!

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Where are we?
• Pattern Matching for instanceof
• Pattern Matching for Switch
• Record and Array Pattern Matching
• Match
• Literals

Deep Dive Java 17 Devoxx UK

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