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

https://twitter.com/JosePaumard
https://github.com/JosePaumard
https://www.youtube.com/c/JosePaumard01
https://www.youtube.com/user/java
https://www.youtube.com/hashtag/jepcafe
https://fr.slideshare.net/jpaumard
https://www.pluralsight.com/authors/jose-paumard
https://jchateau.org

https://twitter.com/JosePaumard
https://github.com/JosePaumard
https://www.youtube.com/c/JosePaumard01
https://www.youtube.com/user/java
https://www.youtube.com/hashtag/jepcafe
https://fr.slideshare.net/jpaumard
https://www.pluralsight.com/authors/jose-paumard
https://dev.java

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
4
Dev.java
Java 8 Java 11

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
5
Java 17 – LTS !
Java 8 Java 11

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
6
OpenJDK?
https://openjdk.java.net

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
7
New Release Cadence!
11
12
13
14
15
16
17
18
19
20
21
22
23
2018 2019 2020 2021 2022 2023 2024 2025
http://jdk.java.net/

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
8
New Release Cadence!
11
12
13
14
15
16
17
18
19
20
21
22
http://jdk.java.net/
23
2018 2019 2020 2021 2022 2023 2024 2025

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
9
New Release Cadence!
11
12
13
14
15
16
17
18
19
20
21
22
https://www.oracle.com/java/
technologies/javase-
downloads.html
23
2018 2019 2020 2021 2022 2023 2024 2025

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
10
New New Release Cadence!
11
12
13
14
15
16
17
18
19
20
21
22
1) LTS: 3 years  2 years
23
2018 2019 2020 2021 2022 2023 2024 2025
https://mreinhold.org/blog/forward-even-faster
https://blogs.oracle.com/java/post/
moving-the-jdk-to-a-two-year-lts-cadence

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
11
New New Release Cadence!
11
12
13
14
15
16
17
18
19
20
21
22
2018 2019 2020 2021 2022 2023 2024 2025
23
1) LTS: 3 years  2 years
https://mreinhold.org/blog/forward-even-faster
https://blogs.oracle.com/java/post/
moving-the-jdk-to-a-two-year-lts-cadence

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
12
New New Release Cadence!
11
12
13
14
15
16
17
18
19
20
21
22
2018 2019 2020 2021 2022 2023 2024 2025
23
1) LTS: 3 years  2 years
2) Free licence (dev + prod)
3) No click-through
https://blogs.oracle.com/java/post/
free-java-license

Sept.
2021
Mars
2014
4
Years
90
80
70
60
50
40
30
20
10
0
56
91
12
17
8
5
16
14
17
14
Mars
2018 3
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
13

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
Copyright © 2021, Oracle and/or its affiliates
14
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

11/2/2021
Copyright © 2021, Oracle and/or its affiliates | Confidential: Internal/Restricted/Highly Restricted
15
Tools

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
Copyright © 2021, Oracle and/or its affiliates
16
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
Tools
jshell
jlink
jdeps
jpackage
java source code launcher
javadoc search + API history

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
17
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

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
18
Step 2: Add 3rd party dependencies
Launching Single File Source Code
public class HelloWorld {
public static void main(String[] args) {
System.out.println(RandomUtils.nextInt());
}
}
$ java -cp /path/to/commons-lang3-3.12.0.jar HelloWorld.java

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
19
Step 3: Execute a shebang file
Launching Single File Source Code
#!/path/to/your/bin/java --source 17
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
$ ./HelloWorld

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
20
Create a runtime image
JLink: Creating Custom Runtime Images
$ jlink
--module-path mods
--add-modules org.mycompany.mymodule
--output myapp-image

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
21
Create a runtime image with a launcher
JLink: Creating Custom Runtime Images
# 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

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
22
The smallest runtime image
JLink: Creating Custom Runtime Images
$ jlink
--add-modules java.base
--output jdk.base
$ du –sh jdk.base jdk-17
40M jdk.base
288M jdk-17

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
23
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
24
API

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
Copyright © 2021, Oracle and/or its affiliates
25
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
Libraries
HTTP client
Collection factories
Unix-domain sockets
Stack walker
Deserialization filtering
Pseudo-RNG, SHA-3, TLS 1.3

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
26
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();

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
27
Step 2: create a client
HttpClient API
HttpClient client =
HttpClient.newBuilder()
.version(HttpClient.Version.HTTP_1_1)
.connectTimeout(Duration.ofSeconds(20))
.build();

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
28
Step 3: send the request
HttpClient API
HttpResponse<InputStream> response =
client.send(request,
HttpResponse.BodyHandlers.ofInputStream());
InputStream inputStream = response.body();

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
29
Step 3: send the request
HttpClient API
HttpResponse<Stream<String>> response =
client.send(request,
HttpResponse.BodyHandlers.ofLines());
Stream<String> lines = response.body();

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
30
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.

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
31
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()

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
32
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);

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
33
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);

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
34
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

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
35
Stack Frame Walker
StackWalker walker =
StackWalker.getInstance(
StackWalker.Option.RETAIN_CLASS_REFERENCE);
walker.forEach(
stackFrame -> System.out.println(stackFrame.getClassName()));

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
36
Stack Frame Walker
Set<String> classNames = ...;
Optional<String> className = walker.walk(
stackFrameStream -> stackFrameStream
.map(StackWalker.StackFrame::getClassName)
.filter(classNames::contains)
.findFirst()
);

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
Copyright © 2021, Oracle and/or its affiliates
37
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
Language
Type inference for locals (var)
Switch expressions
Text blocks
Record classes
Sealed classes
Pattern matching for instanceof

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
38
Do not override finalize()
Stop doing that!
@Deprecated(since="9")
protected void finalize() throws Throwable {
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
39
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);
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
40
☕ Coffee Break!

Record and Array Pattern Matching
Record
Sealed Classes
Switch Expression
Constant Dynamic
Inner Classes
private in VM
Nestmates
Pattern Matching for instanceof
11
14
16
17 Switch on Patterns
18

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
42
In reference to the Amber by Roger
Zelazny
Project Amber

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
43
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

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
44
String name = type pattern
String = le nom du pattern
name = binding variable
o = target operand
Type Pattern
if (o instanceof String name) {
// some code
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
45
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) {}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
46
Record Deconstruction
if (o instanceof Rectangle rectangle) {
int width = rectangle.width();
int height = rectangle.height();
// do something with width and height
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
47
Un record pourra être « déconstruit »
width et height deviennent des binding variables
Record Deconstruction
if (o instanceof Rectangle(int width, int height)) {
// do something with width and height
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
48
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);
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
49
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 -> ...;
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
50
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 {}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
51
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 {}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
52
The default case becomes useless = total switch
Pattern Matching for Switch + Sealed Types
double area = switch(shape) {
case Square(int edge) -> edge* edge;
case Circle(int radius) -> Math.PI*radius*radius;
// default -> ...;
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
53
Record Deconstruction (Again)
if (o instanceof Rectangle rectangle) {
int width = rectangle.width();
int height = rectangle.height();
// do something with width and height
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
54
A record can be « deconstructed »
width et height become binding variables
Record Deconstruction (Again)
if (o instanceof Rectangle(int width, int height)) {
// do something with width and height
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
55
Array Pattern Matching
if (o instanceof String[] array && array.length() >= 2) {
// do something with array[0] and array[1]
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
56
Array Pattern Matching
if (o instanceof String[] {String s1, String s2}) {
// do something with s1 and s2
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
57
Array Pattern Matching
if (o instanceof Circle[] {Circle(var r1), Circle(var r3)}) {
// do something with r1 and r2
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
58
Record 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 -> ...;
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
59
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 {}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
60
You can tell that you do not need a binding variable
Syntaxic Sugars
if (shape instanceof Circle(var center, _)) {
// center and radius are binding variables
}
record Point(int x, int y) {}
record Circle(Point center, int radius) implements Shape {}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
61
You can nest patterns (nested patterns)
Syntaxic Sugars
if (shape instanceof Circle(var center, _) &&
center instanceof Point(int x, int y)) {
// center and radius are binding variables
}
if (shape instanceof Circle(Point(int x, int y), _)) {
// center and radius are binding variables
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
62
The deconstruction uses the canonical constructor of a record
What about:
- factory methods?
- classes that are not records?
Deconstruction

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
63
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) {}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
64
Then this code becomes possible:
Deconstruction Using Factory Methods
double area = switch(shape) {
case Shape.circle(double radius) -> Math.PI*radius*radius;
case Shape.square(double edge) -> edge*edge;
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
65
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!

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
66
You saw patterns with instanceof and switch
Let us see match !
Pattern with Match
record Point(int x, int y) {}
record Circle(Point center, int radius) implements Shape {}
Circle circle = ...;
match Circle(var center, var radius) = circle;
// center and radius are binding variables

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
67
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");
// center and radius are binding variables

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
68
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
}
// center and radius are binding variables

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
69
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;

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
70
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
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
71
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

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
72
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
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
73
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
}

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
74
• 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

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
75
• 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
Patterns at a Glance

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
76
« 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!

11/2/2021
Copyright © 2021, Oracle and/or its affiliates |
77
Where are we?
• Pattern Matching for instanceof
• Pattern Matching for Switch
• Record and Array Pattern Matching
• Match
• Literals
Patterns at a Glance