From Java 11 to 17 and beyond.pdf

From Java 11 to Java 17 and Beyond
Among other things
José Paumard
@JosePaumard
Java Developer Advocate
Java Platform Group

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

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Copyright © 2021, Oracle and/or its affiliates |
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https://dev.java/

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https://dev.java/community/

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https://inside.java/

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Java 17 – LTS!
Java 8 Java 11

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Java 17 – LTS!
Java 8
Java 11
Java 17 ?

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Next LTS: Java 21
Java 8
Java 11
Java 17
Java 21

Language
Type inference for locals (var)
Switch expressions
Text blocks
Record classes
Sealed classes
Pattern matching for instanceof
Compact String, Indify Concatenation
JDK 17: New Features Since the JDK 8
Copyright © 2021, Oracle and/or its affiliates
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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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Stop doing that!

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Do not call new Integer(...)
Stop Calling Wrapper Classes Constructors!
@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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Do not override finalize()
Stop Overriding Finalize!
@Deprecated(since="9", forRemoval=true)
protected void finalize() throws Throwable {
}

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Strings

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A new way of writing Strings
Text Blocks
String message = """
Hello world!""";

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String Templates (prev.)

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Interpolating strings from a template and variables
String Templates (prev.)
String name = "world";
String message = STR."Hello {name}!";
System.out.println(message);
> Hello world!

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Is a String Template Expression
STR is a template policy
"Hello {name}!" is a template with an embedded
expression
The evaluation produces a String, but not always
String Template Expression
String message = STR."Hello {name}!";

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Embedded expressions are expressions
int x = 10, y = 20;
String result = STR."{x} + {y} = {x + y}";
System.out.println(result);
> 10 + 20 = 30

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String result = STR."We have a {getOfferType()} for you";
System.out.println(result);
> We have a gift for you

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String time = STR."The time is {
// The java.time.format package is very useful
DateTimeFormatter
.ofPattern("HH:mm:ss")
.format(LocalTime.now())
} right now";
System.out.println(time);
> The time is 12:34:56 right now

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int index = 10;
String data = STR."{index++} {index++} {index++}";
System.out.println(data);
> 10 11 12

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FMTR: formatter template policy
More Template Policies
String form = FMTR."""
Desc Unit Qty Amount
%-10s{description} $%5.2f{price} %5d{quantity} $%5.2f{price * quantity}
Subtotal $%5.2f{price * quantity}
Tax $%5.2f{price * quantity * tax}
Total $%5.2f{price * quantity * (1.0 + tax)}
""";
System.out.println(form);

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FMTR: formatter template policy
More Template Policies
Desc Unit Qty Amount
hammer $ 7.88 3 $23.64
Subtotal $23.64
Tax $ 3.55
Total $27.19

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Yes!
A policy is a class that implements TemplatePolicy
It supports validation to prevent injection
It can return any object
User Defined Policies?

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Records

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Short answer: a class!
Less short answer: a class
- That extends the Record class
- That is final
What is a Record?

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And you can write:
I Need to Write a Record!
public record User(String name, int age) { }
User sarah = new User("Sarah", 23);
System.out.println(sarah);
$ User[name=Sarah, age=23]

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1) A constructor
2) Accessors: name() and age()
3) The following methods: toString(), equals(),
hashCode()
What Do you Get with a Record?

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You cannot extend a record
A record cannot extend anything
You cannot create any instance field in a record
You can implement interfaces
You can add any instance method
You can add any static field or method
Restrictions on Records

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name and age are the components of the record
Components are both final instance fields
And accessors
Components of a Record

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More on Components
User user = new User("Sarah", 23);
Class<User> userClass = User.class;
boolean isRecord = userClass.isRecord();
Component[] components = userClass.getRecordComponents();

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More on Components
User user = new User("Sarah", 23);
RecordComponent nameComponent = components[0];
Class<?> declaring = nameComponent.getDeclaringRecord();
String name =
(String) nameComponent.getAccessor()invoke(user);

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More on Components
public record User(@UserName String name, int age) { }
@Target(ElementType.RECORD_COMPONENT)
@interface UserName {}

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The state of a record is entirely defined by its components
- You cannot add more state by extension, or by extending
anything
- You cannot add any instance field
Record State

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The constructor of a record that takes its components is called
the canonical constructor
Record Building
public record User(String name, int age) {
public record User(String name, int age) {
this.name = name;
this.age = age;
}
}

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Why would you write your own canonical constructor?
1) Defensive copy
Record Building
public record State(List<City> cities) {
public State(List<City> cities) {
this.cities = List.copyOf(cities);
}
}

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In that case, you need to write your own accessor too!
Record Building
public record State(List<City> cities) {
public State(List<City> cities) {
this.cities = List.copyOf(cities);
}
public List<City> cities() {
return List.copyOf(cities);
}
}

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2) Validation
Record Building
public record Range(int begin, int end) {
public Range(int begin, int end) {
if (begin > end) {
throw new IllegalArgumentException("...");
}
this.begin = begin; this.end = end;
}
}

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2) Validation, with the Compact Constructor
Record Building
public Range {
if (begin > end) {
throw new IllegalArgumentException("...");
}
}
}

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A record constructor must call the canonical constructor
Record Building
public Range(int end) {
this.begin = 0;
this.end = end;
}
}

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A record constructor must call the canonical constructor
Record Building
public Range(int end) {
this(0, end);
}
}

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You cannot build a record
without calling
its canonical constructor
Deserialization calls the canonical constructor of a record

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Deserialization calls the canonical constructor of a record
Records are a perfect choice for Data Transport Objects
Record Serialization

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Sealed Types

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Short answer: type (interface, class, abstract class)!
Less short answer: a type
- That declares its subtypes
- That lives in the same package or module as them
What is a Sealed Type?

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A sealed type must declare its extension
Syntax
public sealed interface Shape
permits Square, Rectangle, WeirdShape {
}

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An extension of a sealed type must be:
- final
- or sealed
- or non-sealed
Syntax

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- final
Syntax
public record Square(int edge)
implements Shape { }

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- sealed
Syntax
public sealed class Rectangle
permits ExtendedRectangle { }

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- non-sealed
Syntax
public non-sealed abstract class WeirdShape
{ }

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Pattern Matching

?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 Types
19

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In reference to the Amber Chronicles
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 = the type of the pattern
String = the name of the pattern
name = the binding variable
o = target operand
Type Pattern
if (o instanceof String name) {
// some code
}

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Type Pattern
Sytem.out.println(name.toUpperCase());
}
if (o instanceof String name && name.length() > 0) {
}

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Type Pattern
}
if (!(o instanceof String name)) {
// you cant use name here!
return; // or throw an exception
}

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Record Pattern Matching
(prev Java 19?)

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record User(String name, int age) {}
if (o instanceof User user)) {
String name = user.name();
int age = user.age();
}

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if (o instanceof User(String name, int age))) {
// use name and age
}

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if (o instanceof User(String name, int age) user)) {
// use name and age
}

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Record deconstruction is easy because a record is built on
components
And components are declared along with it
The binding variables are initialized by calling the accessors
Deconstructing a Record

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Array Pattern Matching

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

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

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Nesting Patterns + Type Inference
if (o instanceof Circle[] {Circle(var r1), Circle(var r2)}) {
// do something with s1 and s2
}
record Circle(int radius) {}

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if (o instanceof Circle[] {
Circle(Point(int x1, int y1), _),
Circle(Point(int x2, int y2), _)}) {
// do something with x1, y1, x2, y2
}
record Circle(Point p1, int radius) {}
record Point(int x, int y) {}

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Pattern Matching for Switch

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interface Shape {}
record Square(int edge) implements Shape {}
record Circle(int radius) implements Shape {}

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double area(Shape shape) {
return switch (shape) {
case Square square ->
square.edge()*square.edge();
case Circle circle ->
Math.PI*circle.radius()* circle.radius();
default -> 0;
}
}

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Switch on a Sealed Type
sealed interface Shape permits Square, Circle {}
record Square(int edge) implements Shape {}
record Circle(int radius) implements Shape {}

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// default -> 0; // Not needed!
}
}

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The compiler can:
- check if a type is not present and raise an error
- raise a warning if an uneeded default is present

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Guarded Pattern (prev. 17 and 18)
case Square square && square.edge() == 0 -> 0;
}
}

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Guarded Pattern (prev. 17 and 18)
case Square square && square.edge() == 0 -> 0;
}
}

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Switch Pattern with When (prev. 19?)
case Square square when square.edge() == 0 -> 0;
}
}

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(19 prev?)
Switch and Record Pattern Matching
case Square(int edge) when edge == 0 -> 0;
case Square(int edge) -> edge*edge;
case Circle(int radius) -> Math.PI*radius*radius;
}
}

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The Future of Pattern Matching

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Nested Patterns, needed binding variables, type inference
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), _)) {
}

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The deconstruction uses the canonical constructor of a record
What about:
- factory methods?
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 could become possible:
double area = switch(shape) {
case Shape.circle(double radius) -> Math.PI*radius*radius;
case Shape.square(double edge) -> edge*edge;
}

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With factory methods
if (opt instanceof Optional.of(var max)) {
// max is a binding variable
}

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With factory methods
if (s instanceof
String.format("%s is %d years old",
String name, Integer.valueOf(int age) {
// name and age are binding variables
}

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Map deconstruction
This is an extended form of Pattern Matching where you check
the value of a binding variable
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.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("street", 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
// age is a deconstructed int
}

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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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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;
}
}
This is the output of the
deconstructor
It allows both:
- overloading
- defensive copy

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Match can check if an expression matches a pattern
Just as if checks for a boolean expression
Introducing Match

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Pattern with Match (or Let?)
record Circle(Point center, int radius) implements Shape {}
Circle circle = ...;
match Circle(var center, var radius) = circle;

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Pattern with Let
let Circle(var center, var radius) = circle
else
throw new IllegalStateException("Not a circle");

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Pattern with Let
let Circle(var center, var radius) = circle
else {
center = new Point(0, 0); // this is called
radius = 0; // an anonymous matcher
}

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

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List<Point> points = ...;
for (Point point: points) {
int x = point.x();
int y = point.x();
// do something with x and y
}

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List<Point> points = ...;
for (Point(int x, int y): points) {
// do something with x and y
}

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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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Where are we?
• Pattern Matching for instanceof (16)
• Pattern Matching for Switch (prev 17, 18, 19?)
• Record and Array Pattern Matching (19?)
• Match
• Literals

From Java 11 to 17 and beyond.pdf

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From Java 11 to 17 and beyond.pdf