Evolution and Examples of Java Features, from Java 1.7 to Java 22

Yann-Gaël Guéhéneuc
(/jan/, he/il)
Work licensed under Creative Commons
BY-NC-SA 4.0 International
New Java
yann-gael.gueheneuc@concordia.ca
Version 0.22.1
2024/03/28

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Patrick Naughton
Scott McNealy
Mike Sheridan James Gosling
1991

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Naming
 Java
– 1995/05/23
– Language
 JDK (Java Development Kit)
– Compiler (Java Language Specification)
– VM (Java Virtual Machine Specification)
– APIs/Libraries (Java Class Libraries)

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Process
 JCP: Java Community Process
– Established in 1998
– JSR-387 describes JCP v2.11

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Documents
 JLSs: Java Language Specifications
– What is Java
 JSRs: Java Specification Requests
– Parts of the JCP
– New specifications and technologies
– JDK/OpenJDK
 JEPs: Java Enhancement Proposals
– Experimental ideas
– Could become JSRs
https://stackoverflow.com/questions/51282326/what-is-the-difference-or-relation-between-jls-jsr-and-jep

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Too
Many
Features
Disclaimer
No
Preview
No
Incubator

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Organisation
 Per release
– With some cross-references
 Three categories
– Language
– JVM
– APIs
Misc
+

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Java 5
Java 6
2004/09/30
2006/12/11

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Enums
 Special data type
– Declares/defines
variables set to
constants
interface PseudoEnum0 {
int YES = 0;
int NO = 1;
}
interface Interface1 {
public boolean foo();
}
enum RealEnum1 implements Interface1 {
YES {
public boolean foo() {
return true;
}
},
NO {
return false;
}
};
public boolean bar() {
return this.foo();
}
}

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Enums
 Based on anonymous classes
System.out.println(RealEnum1.YES.bar());
System.out.println(RealEnum1.NO.bar());
System.out.print("Superclass: ");
System.out.println(RealEnum1.NO.getClass().getSuperclass());
System.out.print("Class: ");
System.out.println(RealEnum1.NO.getClass());
for (final Method method : RealEnum1.NO.getClass().getDeclaredMethods()) {
System.out.print("tMethods: ");
System.out.println(method);
}

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Enums
 Based on anonymous classes
System.out.println(RealEnum1.YES.bar());
System.out.println(RealEnum1.NO.bar());
System.out.print("Superclass: ");
System.out.println(RealEnum1.NO.getClass().getSuperclass());
System.out.print("Class: ");
System.out.println(RealEnum1.NO.getClass());
for (final Method method : RealEnum1.NO.getClass().getDeclaredMethods()) {
System.out.print("tMethods: ");
System.out.println(method);
}
true
false
Superclass: class net.ptidej.newjava.enums.RealEnum1
Class: class net.ptidej.newjava.enums.RealEnum1$2
Methods: public boolean net.ptidej.newjava.enums.RealEnum1$2.foo()

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Enums
Enum Simulated Enum
}
YES {
return true;
}
},
NO {
return false;
}
};
return this.foo();
}
}
}
abstract class SimulatedEnum1 implements Interface1 {
public static final SimulatedEnum1 YES =
new SimulatedEnum1() {
@Override
return true;
}
};
public static final SimulatedEnum1 NO =
@Override
return false;
}
};
private SimulatedEnum1() {
}
return this.foo();
}
}

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Enums
Enum Simulated Enum
}
YES {
return true;
}
},
NO {
return false;
}
};
return this.foo();
}
}
}
@Override
return true;
}
};
@Override
return false;
}
};
}
return this.foo();
}
}
Instances of two
anonymous classes

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Enums
Enum Simulated Enum
}
YES {
return true;
}
},
NO {
return false;
}
};
return this.foo();
}
}
Why private?
}
@Override
return true;
}
};
@Override
return false;
}
};
}
return this.foo();
}
}
Instances of two
anonymous classes

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Enums
 More than just syntactic sugar
– Constants are constant expressions
final RealEnum3 v = // ...
switch (v) {
case YES:
System.out.println("YES");
break;
case NO:
System.out.println("NO");
break;
default:
throw // ...
}
final SimulatedEnum3 v1 = // ...
switch (v1) {
case SimulatedEnum3.YES:
break;
case SimulatedEnum3.NO:
break;
default:
throw // ...
}

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Enums
 More than just syntactic sugar
– Constants are constant expressions
final RealEnum3 v = // ...
switch (v) {
case YES:
break;
case NO:
break;
default:
throw // ...
}
switch (v1) {
break;
break;
default:
throw // ...
}
case expressions must be constant expressions

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Enums
 No work around the compilation error
– Some constants are not constant expressions
switch (v1) {
break;
break;
default:
throw // ...
}
final int v2 = // ...
switch (v2) {
case SimulatedEnum3.YES.constantID:
break;
case SimulatedEnum3.NO.constantID:
break;
default:
throw // ...
}
public final int constantID;

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Java 7
2011/07/07
2011/07/07

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Strings in switch
https://www.baeldung.com/java-switch
public String exampleOfSwitch(String animal) {
String result;
switch (animal) {
case "DOG" :
result = "domestic animal";
break;
case "CAT" :
result = "domestic animal";
break;
case "TIGER" :
result = "wild animal";
break;
default :
result = "unknown animal";
break;
}
return result;
}

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try With Resources
 New interfaces
– java.lang.Closeable
– java.lang.AutoCloseable
https://www.baeldung.com/java-try-with-resources
try (final Scanner scanner = new Scanner(new File("test.txt"))) {
while (scanner.hasNext()) {
System.out.println(scanner.nextLine());
}
}
catch (final FileNotFoundException fnfe) {
fnfe.printStackTrace();
}

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Diamond Operator <>
https://www.baeldung.com/java-diamond-operator
List<String> cars = new ArrayList<String>();
List<String> cars = new ArrayList<>();
vs.

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Vargs in Method Declaration
https://www.baeldung.com/java-varargs
https://www.baeldung.com/java-varargs
public String format() {
// ...
}
public String format(String value) {
//...
}
public String format(String val1, String val2) {
// ...
}
public String formatWithVarArgs(String... values) {
System.out.println(values[0]);
// ...
}
vs.

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Binary Integer Literals
https://www.geeksforgeeks.org/java-program-to-illustrate-use-of-binary-literals/
// Byte type Binary Literal
byte a1 = 0b011;
// Short type Binary Literal
short b1 = 0b101;
// Int type Binary literal
int c1 = 0b011;
// Long type Binary literal
long d1 = 0b0000011111100011;

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Underscores in Numeric Literals
int i = 12_34_56;
System.out.println(i);
https://www.geeksforgeeks.org/using-underscore-numeric-literals-java/

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Multiple Exception Types
 Multiple exception types
 Multiple exceptions rethrown
with improved type checking

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Multiple Exception Types
public static void main(final String[] args) {
try {
Example1.rethrow("abc");
}
catch (final FirstException | SecondException e) {
// Below assignment would throw a compile-time exception, e is implicitly final
// e = new Exception();
System.out.println(e.getMessage());
}
}
private static void rethrow(final String s) throws FirstException, SecondException {
try {
if (s.equals("First")) throw new FirstException("First");
else throw new SecondException("Second");
}
catch (final Exception e) {
// Below assignment would disable improved rethrow exception type checking
// e = new ThirdException();
throw e;
}
}
private static class FirstException extends Exception {
public FirstException(String msg) {
super(msg);
}
}
// ...

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JSR-292: invokedynamic
 invokestatic, for class methods
 invokevirtual, for instance methods
 invokeinterface, for interface methods
 invokespecial, for instance initialisation,
superclass, and private methods

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Gilad Bracha, 2005

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 invokedynamic indicates that a dynamic
language run-time specific call occurs
 The call occurs through MethodHandle(s)
https://www.baeldung.com/java-method-handles
MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
MethodType mt = MethodType.methodType(String.class, char.class, char.class);
MethodHandle replaceMH = publicLookup.findVirtual(String.class, "replace", mt);
String output = (String) replaceMH.invoke("jovo", 'o', 'a');

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JSR-166: Concurrency Utilities
 Concurrency utilities under JSR 166
 java.util.concurrent wants to be for
concurrency what java.util.Collections
is for collections
 With some JVM support
– Timing
– Atomics
– …
https://gee.cs.oswego.edu/dl/concurrency-interest/jsr166-slides.pdf

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https://www.uml-diagrams.org/java-7-concurrent-uml-class-diagram-example.html

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final Runnable runnable1 = new RunnableExample("executor.execute(...)");
final ExecutorService executor = Executors.newFixedThreadPool(10);
executor.execute(runnable1);
final Runnable runnable2 = new RunnableExample("new Thread(...)");
new Thread(runnable2).start();
vs.

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class ImageRenderer {
Image render(final byte[] raw) {
return // ...
}
}
public class Example2 {
public void display(final byte[] raw) throws InterruptedException, ExecutionException {
final ImageRenderer renderer = new ImageRenderer();
final Future<Image> image = executor.submit(new Callable<Image>() {
public Image call() {
return renderer.render(raw);
}
});
drawBorders(); // do other things ...
drawCaption(); // ... while executing
drawImage(image.get()); // use Future
}
// ...

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public void run() {
synchronized (this.resource) {
this.resource.doSomething();
}
this.resource.doLogging();
}
public void run() {
try {
if (this. lock.tryLock(10, TimeUnit.SECONDS)) {
this.resource.doSomething();
}
}
catch (final InterruptedException exception) {
exception.printStackTrace();
}
finally {
this.lock.unlock();
}
this.resource.doLogging();
}
vs.
https://www.digitalocean.com/com
munity/tutorials/java-lock-example-
reentrantlock

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https://www.geeksforgeeks.org/semaphore-in-java/
private final Semaphore semaphore;
private void connect(final String user)
throws InterruptedException {
System.out.println(getCurrentDateTime()
+ " : " + user + " waiting sem");
this.semaphore.acquire();
+ " : " + user + " acquired sem");
Thread.sleep(1000); // Some work...
this.semaphore.release();
+ " : " + user + " released sem");
}
https://mkyong.com/java/java-semaphore-examples/

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https://www.geeksforgeeks.org/atomic-variables-in-java-with-examples/
class Counter extends Thread {
private final AtomicInteger count;
public Counter() {
this.count = new AtomicInteger();
}
public void run() {
final int max = 10_000_000;
for (int i = 0; i < max; i++) {
count.addAndGet(1);
}
}
public int getCount() {
return this.count.get();
}
}

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JSR-203: New File I/O Library
 Extensive File I/O API
 Socket channel API
 Asynchronous I/O API

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 Extensive File I/O API
https://www.baeldung.com/java-nio2-file-visitor
public class Example1FileVisitor {
public static void main(final String[] args) throws IOException {
final Path startPath = Paths.get("D:DocumentsTutorials220926 - New Java");
final String fileName = "Example1FileVisitor.java";
final FileVisitorImpl visitor = new FileVisitorImpl(fileName, startPath);
Files.walkFileTree(startPath, visitor);
}
}

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class FileVisitorImpl implements FileVisitor<Path> {
private final String fileName;
private final Path startPath;
public FileVisitorImpl(final String aFileName, final Path aStartPath) {
this.fileName = aFileName;
this.startPath = aStartPath;
}
@Override
public FileVisitResult preVisitDirectory(final Path aPath, final BasicFileAttributes someAttributes) {
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult visitFile(final Path aPath, final BasicFileAttributes someAttributes) {
final String fileName = aPath.getFileName().toString();
if (fileName.equals(this.fileName)) {
return FileVisitResult.TERMINATE;
}
}
@Override
public FileVisitResult visitFileFailed(final Path aPath, final IOException anIOException) {
}
@Override
public FileVisitResult postVisitDirectory(final Path aPath, final IOException anIOException) {
try {
if (Files.isSameFile(aPath, this.startPath)) {
return FileVisitResult.TERMINATE;
}
} catch (final IOException e) {
e.printStackTrace();
}
}
}

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 Socket channel API – Client
public static void client() throws IOException {
final ServerSocketChannel serverSocket = ServerSocketChannel.open();
serverSocket.socket().bind(new InetSocketAddress(9000));
final SocketChannel client = serverSocket.accept();
System.out.println("Connection set: " + client.getRemoteAddress());
final Path path = Paths.get("D:DocumentsTutorials220926 - New JavaReceivedFile.txt");
final FileChannel fileChannel = FileChannel.open(
path,
EnumSet.of(StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING,
StandardOpenOption.WRITE));
final ByteBuffer buffer = ByteBuffer.allocate(1024);
while (client.read(buffer) > 0) {
buffer.flip();
fileChannel.write(buffer);
buffer.clear();
}
fileChannel.close();
System.out.println("File received");
client.close();
}
https://www.tutorialspoint.com/java_nio/java_nio_socket_channel.htm

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 Socket channel API – Server
public static void server() throws IOException {
final SocketChannel server = SocketChannel.open();
final SocketAddress socketAddr = new InetSocketAddress("localhost", 9000);
server.connect(socketAddr);
final Path path = Paths.get("D:DocumentsTutorials220926 - New JavaPatterns.txt");
final FileChannel fileChannel = FileChannel.open(path);
final ByteBuffer buffer = ByteBuffer.allocate(1024);
while (fileChannel.read(buffer) > 0) {
buffer.flip();
server.write(buffer);
buffer.clear();
}
fileChannel.close();
System.out.println("File sent");
server.close();
}

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 Socket channel API – Main
final Runnable runnableClient = new Runnable() {
public void run() {
try {
Example2SocketChannel.client();
}
}
};
final Runnable runnableServer = new Runnable() {
public void run() {
try {
Example2SocketChannel.server();
}
}
};
executor.execute(runnableClient);
executor.execute(runnableServer);
}

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 Asynchronous I/O API
“The asynchronous channel APIs were
introduced into the existing
java.nio.channels package […] by
prefixing […] with Asynchronous”

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Translucent and Shaped Windows
 Improves Java Swing
 Allow new, nicer themes
https://ateraimemo.com/Swing/TranslucentFrame.html
Window.setShape(Shape s)
Window.setOpacity(float f)

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Network Protocols
 Network protocols
– Stream Control
Transport Protocol
(SCTP)
– Sockets Direct
Protocol (SDP)
 In packages
– com.sun.nio.sctp
– com.sun.sdp
https://www.oracle.com/technical-resources/articles/javase/sctp.html
final SctpServerChannel ssc =
SctpServerChannel.open();
final InetSocketAddress serverAddr = // ...
ssc.bind(serverAddr);
while (true) {
final SctpChannel sc = ssc.accept();
final Date today = new Date();
cbuf.put(USformatter.format(today)).flip();
encoder.encode(cbuf, buf, true);
buf.flip();
messageInfo.streamNumber(FUS_STREAM);
sc.send(buf, messageInfo);
buf.clear();
cbuf.clear();
cbuf.put(FRformatter.format(today)).flip();
encoder.encode(cbuf, buf, true);
buf.flip();
messageInfo.streamNumber(FR_STREAM);
sc.send(buf, messageInfo);
buf.clear();
cbuf.clear();
// ...

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Updates to XML and Unicode
 New system property named
org.jcp.xml.dsig.secureValidation
 New XML Processing Limits
 Regular Expression pattern matching
supports Unicode 6.0.0
– Major version of the Unicode Standard

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default, static Interface Methods
public interface IA {
int foo();
default int bar() {
return 42;
}
}
final IA anIA = new IA() {
public int foo() {
return 0;
}
};
System.out.println(anIA.foo());
System.out.println(anIA.bar());
final IA anotherIA = new IA() {
public int foo() {
return IA.super.bar();
}
public int bar() {
return 0;
}
};
System.out.println(anotherIA.foo());
System.out.println(anotherIA.bar());
}

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int foo();
default int bar() {
return 42;
}
}
public int foo() {
return 0;
}
};
public int foo() {
return IA.super.bar();
}
public int bar() {
return 0;
}
};
}
0
42
42
0

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 https://stackoverflow.c
om/questions/512877/
why-cant-i-define-a-
static-method-in-a-
java-interface
int foo();
static int bar() {
return 42;
}
}
public class A {
int foo() {
return 0;
}
static int bar() {
return 42;
}
}
public int foo() {
return 0;
}
};
final A anA = new A();
System.out.println(anA.foo());
System.out.println(anA.bar());
}

60/360
static-method-in-a-
java-interface
int foo();
static int bar() {
return 42;
}
}
public class A {
int foo() {
return 0;
}
static int bar() {
return 42;
}
}
public int foo() {
return 0;
}
};
}

61/360
static-method-in-a-
java-interface
int foo();
static int bar() {
return 42;
}
}
public class A {
int foo() {
return 0;
}
static int bar() {
return 42;
}
}
public int foo() {
return 0;
}
};
}
System.out.println(IA.bar());

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JSR-335, JEP-126: λ Expressions
 λ Expressions
interface Applicable<T, R> {
public R apply(final T aParameter);
}
final Applicable<String, Integer> strlen = new Applicable<>() {
@Override
public Integer apply(final String aParameter) {
return aParameter.length();
}
};
System.out.println(strlen.apply("Hello, World!"));
}
https://jenkov.com/tutorials/java-functional-programming/functional-interfaces.html

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


}
@Override
}
};
}

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 Lots of boilerplate code
 Difficult to understand
 Not common in the libraries
}
@Override
}
};
}

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 Solution
– Simple syntactic sugar
– Set of functional interfaces
– Libraries using these interfaces

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 Solution

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 Solution
}
final Applicable<String, Integer> strlen = (paramter) -> paramter.length();
}

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 Solution
}
final Applicable<String, Integer> strlen = (paramter) -> paramter.length();
}
final Applicable<String, Integer> strlen = String::length;
}

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 Solution
http://blog.orfjackal.net/2014/07/java-8-functional-interface-naming-guide.html

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 Solution
http://blog.orfjackal.net/2014/07/java-8-functional-interface-naming-guide.html

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 Solution
https://blogs.oracle.com/javamagazine/post/functional-programming-in-java-part-1-lists-lambdas-and-method-references

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 Solution
https://blogs.oracle.com/javamagazine/post/functional-programming-in-java-part-1-lists-lambdas-and-method-references
final List<String> friends = Arrays.asList("Rick Deckard", "Roy Batty", "Harry
Bryant", "Hannibal Chew", "Gaff", "Holden", "Leon Kowalski", "Taffey Lewis",
"Pris", "Rachael", "J.F. Sebastian", "Dr. Eldon Tyrell", "Zhora", "Hodge",
"Mary");
for (int i = 0; i < friends.size(); i++) {
System.out.println(friends.get(i));
}
for (String name : friends) {
System.out.println(name);
}
friends.forEach(new Consumer<String>() {
public void accept(final String aName) { System.out.println(aName); }});
friends.forEach((final String name) -> System.out.println(name));
friends.forEach((name) -> System.out.println(name));
friends.forEach(name -> System.out.println(name));
friends.forEach(System.out::println);
friends.stream().map(String::toUpperCase).forEach(
name -> System.out.print(name + " "));
System.out.println();
final List<String> namesStartingWithN = friends.stream().
filter(name -> name.startsWith("R")).collect(Collectors.toList());
System.out.println(namesStartingWithN);

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 But code duplication!
https://blogs.oracle.com/javamagazine/post/functional-programming-
in-java-part-2-lambda-reuse-lexical-scoping-and-closures-and-reduce
output = friends1.stream().filter(name -> name.startsWith("R")).collect(Collectors.toList());
System.out.println(output);
output = friends2.stream().filter(name -> name.startsWith("R")).collect(Collectors.toList());
final Predicate<String> predicate = name -> name.startsWith("R");
output = friends1.stream().filter(predicate).collect(Collectors.toList());
output = friends2.stream().filter(predicate).collect(Collectors.toList());
vs.

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// Lexical scoping and closure
output = friends1.stream().filter(checkIfStartsWith("R")).collect(Collectors.toList());
output = friends2.stream().filter(checkIfStartsWith("P")).collect(Collectors.toList());
// Narrower lexical scoping
final Function<String, Predicate<String>> startsWithLetter = letter -> (name ->
name.startsWith(letter));
output = friends1.stream().filter(startsWithLetter.apply("R")).collect(Collectors.toList());
output = friends2.stream().filter(startsWithLetter.apply("P")).collect(Collectors.toList());
vs.

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output = friends1.stream().filter(startsWithLetter("R")).collect(Collectors.toList());
output = friends2.stream().filter(startsWithLetter("P")).collect(Collectors.toList());
vs.

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https://forum.devtalk.com/t/functional-programming-in-java-second-
edition-p-35-refactoring-to-narrow-the-scope-code/105447
output = friends1.stream().filter(startsWithLetter("R")).collect(Collectors.toList());
output = friends2.stream().filter(startsWithLetter("P")).collect(Collectors.toList());
vs.

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JSR-308, JEP-104: Type Annotations
 Allow pluggable type systems
 Help enforce stronger typing
final String aString = null;
final String anotherString = aString;
System.out.println(anotherString);
}
}

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}
}
final @NonNull String anotherString = aString;
}
}

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}
}
}
}
Null type mismatch: required
'@NonNull String' but the
provided value is null

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}
}
}
}
final String aString = "";
}
}
Null type mismatch: required
'@NonNull String' but the
provided value is null

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class A {
String getString() {
return null;
}
}
public static void foo1() {
final A a = new A();
final String aString = a.getString();
}
if (aString != null) {
}
}
}

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class A {
String getString() {
return null;
}
}
}
if (aString != null) {
}
}
}
Null type safety […] needs
unchecked conversion to
conform to '@NonNull String'

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 “The Checker Framework includes compiler
plug-ins ("checkers") that find bugs or verify
their absence. It also permits you to write
your own compiler plug-ins.”
– https://checkerframework.org/tutorial/

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Unsigned Integer Arithmetic
 Comparison
 Division/Modulo
 Parsing
 Formatting
https://www.baeldung.com/java-unsigned-arithmetic
public static void main(String[] args) {
final int positive = Integer.MAX_VALUE;
final int negative = Integer.MIN_VALUE;
final int signedComparison = Integer.compare(positive, negative);
if (signedComparison > 0) {
System.out.println("Positive > negative (signed comparison)");
}
final int unsignedComparison = Integer.compareUnsigned(positive, negative);
if (unsignedComparison < 0) {
System.out.println("Positive NOT > negative (unsigned comparison)");
}
}
}

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JEP-120: Repeating Annotations
 “Annotations, a form of metadata, provide
data about a program that is not part of the
program [and] have no direct effect on the
operation of the code they annotate.”
https://docs.oracle.com/javase/tutorial/java/annotations/

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 “Annotations, a form of metadata, provide
data about a program that is not part of the
program [and] have no direct effect on the
operation of the code they annotate.”
https://docs.oracle.com/javase/tutorial/java/annotations/

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https://rolyhewage.medium.com/type-annotations-repeating-annotations-in-java-722073df9f99
@Retention(RetentionPolicy.RUNTIME)
@interface ScheduleNonRepeatable1 {
String dayOfMonth() default "First";
String dayOfWeek() default "Mon";
int hour() default 12;
}
@ScheduleNonRepeatable1(dayOfWeek = "Fri", hour = 23)
final Example1 example1 = new Example1();
final Annotation annotation = example1.getClass().
getAnnotation(ScheduleNonRepeatable1.class);
System.out.println(annotation);
}
}

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}
}
}
@ScheduleNonRepeatable1(hour=23, dayOfMonth="First", dayOfWeek="Fri")

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}
@ScheduleNonRepeatable2(dayOfMonth = "last")
}
}

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}
@ScheduleNonRepeatable2(dayOfMonth = "last")
}
}
Duplicate annotation of
non-repeatable type
@ScheduleNonRepeatable2

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@interface Schedules {
ScheduleRepeatable[] value();
}
@Repeatable(Schedules.class)
@interface ScheduleRepeatable {
}
@ScheduleRepeatable(dayOfMonth = "last")
@ScheduleRepeatable(dayOfWeek = "Fri", hour = 23)
getAnnotation(Schedules.class);
}
}

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@interface Schedules {
ScheduleRepeatable[] value();
}
@Repeatable(Schedules.class)
@interface ScheduleRepeatable {
}
@ScheduleRepeatable(dayOfMonth = "last")
@ScheduleRepeatable(dayOfWeek = "Fri", hour = 23)
getAnnotation(Schedules.class);
}
}
@Schedules({@ScheduleRepeatable(hour=12, dayOfMonth="last", dayOfWeek="Mon"),
@ScheduleRepeatable(hour=23, dayOfMonth="First", dayOfWeek="Fri")})

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JEP-178: Statically-linked JNI
Libraries
 Native programs that embed the JRE
 Java programs running in environments
without shared libraries
 Enable developers to package a Java run-
time, native code, and Java code together
into a single binary

95/360
JEP-122: Permanent Generation
Removal
 “Automatic garbage
collection is [..]
identifying which
objects are in use and
[…] deleting the
unused objects.”
 Remove Permanent
Generation
– No more size tuning
https://openjdk.org/jeps/122

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JEP-174: Nashorn JS Engine
 Successor of Mozilla’s Rhino
 100% in ECMAScript v5.1 test suite
 Java 8: Introduced
 Java 11: Deprecated
 Java 15: Removed

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JEP-174: Nashorn JS Engine
 https://github.com/openjdk/nashorn
https://www.baeldung.com/java-nashorn
final ScriptEngine engine = new ScriptEngineManager().getEngineByName("Nashorn");
final Bindings bindings = engine.createBindings();
bindings.put("name", "Nashorn");
result = engine.eval("var greeting = 'hello world' + name;" + "print(greeting);" + "greeting");
System.out.println(result);
final Invocable invocable = (Invocable) engine;
engine.eval("function composeGreeting(name) {" + "return 'Hello ' + name" + "}");
result = invocable.invokeFunction("composeGreeting", "Nashorn");
result = engine.eval("var HashMap = Java.type('java.util.HashMap’);"
+ "var map = new HashMap();"
+ "map.put('hello', 'world');" + "map");

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JSR-310, JEP-150: Date, Time API
 Need to manipulate dates and times
 Disparate APIs, missing features
– Set time to midnight for a date without a time
 Complete terminology
 Complete, cohesive implementation
– java.time.*

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JEP-153: JavaFX Applications
 Three “types” of programs
– Class files
– JAR files
– JavaFX
 Enhance the java command-line to launch
JavaFX programs

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Private Interface Methods
int foo();
default int bar() {
return this.bar1();
}
private int bar1() {
return 42;
}
}
public int foo() {
return 0;
}
};
public int foo() {
return IA.super.bar1();
}
public int bar() {
return 0;
}
};
}

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Private Interface Methods
int foo();
default int bar() {
return this.bar1();
}
private int bar1() {
return 42;
}
}
public int foo() {
return 0;
}
};
public int foo() {
return IA.super.bar1();
}
public int bar() {
return 0;
}
};
}
0
42
42
0

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JSR-376: Modularization
 JSR-376: Java Platform Module System,
part of Project Jigsaw
– Ease library construction, maintenance
– Security, maintainability of Java (and JDK)
– Allow scaling down programs for small devices
– Improve program compilation and loading times
https://openjdk.org/projects/jigsaw/

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 JEP-200: The Modular JDK
 JEP-201: Modular Source Code
 JEP-220: Modular Run-time Images
 JEP-260: Encapsulate Most Internal APIs
 JEP-261: Module System
 JEP-282: jlink: The Java Linker
 JSR 376: Java Platform Module System

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 Classpath / JARs Hell
 Version conflicts
 Large Monolithic JDK
 Security Problems
https://www.geeksforgeeks.org/jpms-java-platform-module-system/

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– Cf. DLL Hell, no versions, one directory
– One, long list of JAR files
• Run-time missing dependencies
• Order of declaration (shadowing)

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– E.g., in Java v1.4.2, RT.jar is 21.8 MB (!)

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– Implementation classes must be public
– Cannot control access to these classes
– padl.kernel vs. padl.kernel.impl

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 A module is a “package of packages”
– With one module descriptor
– With own resources (data)
 A module descriptor
– Domain Specific Language
– exports, module, open, opens, provides,
requires, to, transitive, uses, and with

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Raoul-Gabriel Urma, Mario Fusco, Alan Mycroft ; Modern Java in Action ; Manning, 2018 (Chapter 14)
module com.example.foo {
requires transitive com.example.foo.network;
requires static com.example.foo.http;
requires java.logging;
exports com.example.foo.bar;
exports com.example.foo.internal to
com.example.foo.probe;
opens com.example.foo.quux;
opens com.example.foo.internal to
com.example.foo.network,
uses com.example.foo.spi.Intf;
provides com.example.foo.spi.Data with
com.example.foo.Impl;
}

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Raoul-Gabriel Urma, Mario Fusco, Alan Mycroft ; Modern Java in Action ; Manning, 2018 (Chapter 14)
}

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 Declaration of module
com.example.foo
 Dependencies on
three other modules
– transitive: client
modules also can
access that module
– static: at compile-time,
option at run-time
}

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 (Qualified) exports to
other, client modules
– Public types accessible
to all client modules
– Or only to types in
com.example.foo.probe
}

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 (Qualified) opening to
other, client modules
at run-time only
– Public types accessible
to all client modules
– Or only to types in com.
example.foo.network or
com.example.foo.probe
– Allows introspection
}

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}
 Service consumer
– Interface/abstract class
com.example.foo.spi.Intf
 Service provider
– Interface/abstract class
com.example.foo.spi.Data
– With concrete class
com.example.foo.Impl

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 modularisation.Client
– Can access any public
type at compile-time
and at run-time
– Can access some
protected/private
data with introspection
 internal.Client
– Cannot access
HiddenImplementation

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 modularisation.Client
– Can access any public
type at compile-time
and at run-time
– Can access some
protected/private
data with introspection
 internal.Client
– Cannot access
HiddenImplementation
Package-protected
Class (not public!)

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final Interface aki = new Implementation();
aki.foo();
System.out.println("Call on public implementation: ");
final Class<? extends Interface> implementation1 = Class
.forName(“....impl.Implementation").asSubclass(Interface.class);
final Interface aki1 = implementation1.getDeclaredConstructor().newInstance();
final Method[] methods1 = implementation1.getDeclaredMethods();
for (final Method method : methods1) {
try {
method.setAccessible(true);
method.invoke(aki1, new Object[0]);
} catch (final RuntimeException e) {
System.out.println(e.getMessage());
}
}
final Class<? extends Interface> implementation2 = Class
.forName(“....impl.HiddenImplementation").asSubclass(Interface.class);
final Interface aki2 = implementation2.getDeclaredConstructor().newInstance();
final Method[] methods2 = implementation2.getDeclaredMethods();
for (final Method method : methods2) {
// Same code

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 The client code has access to the fields and
methods in all public types, even if private
Direct call: Implementation.bar()
Call on public implementation:
bar: Implementation.bar()
foo: Implementation.bar()
Call on hidden implementation:
Exception in thread "main" java.lang.IllegalAccessException: class
net.ptidej.modularisation.Client cannot access a member of class
net.ptidej.modularisation.kernel.impl.HiddenImplementation with package
access
...

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 The client code has access to the fields and
methods in all public types, even if private
Exception in thread "main" java.lang.IllegalAccessException: class
net.ptidej.modularisation.Client cannot access a member of class
net.ptidej.modularisation.kernel.impl.HiddenImplementation with package
access
...
Including the
private method

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 Client
 Provider
module ModularizationWithModulesClient1 {
requires ModularizationWithModulesLibrary1;
}
module ModularizationWithModulesLibrary1 {
exports net.ptidej.modularisation.kernel;
exports net.ptidej.modularisation.kernel.impl;
}

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 Client (not a module)
 Client (module)
Exception in thread "main" java.lang.IllegalAccessException: class net.ptidej.modularisation.Client
cannot access a member of class net.ptidej.modularisation.kernel.impl.HiddenImplementation with
package access
bar: Unable to make private void net.ptidej.modularisation.kernel.impl.Implementation.bar()
accessible: module ModularizationWithModulesLibrary1 does not "opens
net.ptidej.modularisation.kernel.impl" to module ModularizationWithModulesClient1
(in module ModularizationWithModulesClient1) cannot access a member of class
net.ptidej.modularisation.kernel.impl.HiddenImplementation (in module
ModularizationWithModulesLibrary1) with package access

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 Client (module)
package access
Non-module can still
access private methods

127/360
 Client (module)
package access
Non-module can still
access private methods
Modules cannot access
private/package data

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 Client
 Provider
module ModularizationWithModulesClient2 {
requires ModularizationWithModulesLibrary2;
uses net.ptidej.modularisation.kernel.Interface;
}
module ModularizationWithModulesLibrary2 {
exports net.ptidej.modularisation.kernel;
provides
net.ptidej.modularisation.kernel.Interface with
net.ptidej.modularisation.kernel.impl.Implementation;
}

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 Client implementation
 Client output
Implementation.bar()
(in module ModularizationWithModulesClient2) cannot access class
net.ptidej.modularisation.kernel.impl.Implementation (in module ModularizationWithModulesLibrary2)
because module ModularizationWithModulesLibrary2 does not export
net.ptidej.modularisation.kernel.impl to module ModularizationWithModulesClient2
final ServiceLoader<Interface> providers = ServiceLoader.load(Interface.class);
final Interface aki = providers.findFirst().orElse(null);
aki.foo();

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 Client implementation
 Client output
Implementation.bar()
(in module ModularizationWithModulesClient2) cannot access class
net.ptidej.modularisation.kernel.impl.Implementation (in module ModularizationWithModulesLibrary2)
because module ModularizationWithModulesLibrary2 does not export
net.ptidej.modularisation.kernel.impl to module ModularizationWithModulesClient2
No access to data not
exported/provided,
even if public!
final ServiceLoader<Interface> providers = ServiceLoader.load(Interface.class);
final Interface aki = providers.findFirst().orElse(null);
aki.foo();

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https://www.baeldung.com/java-illegal-reflective-access
 Backward compatibility

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https://docs.oracle.com/javase%2F9%2Fdocs%2Fapi%2F%2F/overview-summary.html

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https://docs.oracle.com/javase%2F9%2Fdocs%2Fapi%2F%2F/java/lang/Module.html

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 Relation to OSGi
– Open Service Gateway Initiative
• From 05/2000, latest 12/2020
– Eclipse Foundation open-source project
– Framework for developing and deploying
• Modular programs and libraries
• IoT and other constrained devices
https://www.techtarget.com/searchnetworking/definition/OSGi

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OSGi (Bundles)
 Several class loaders
– Cannot be used for the JDK
– Allow “duplicate” packages
– Allow multiple versions
 Visibility
JPMS (Modules)
 One class loader
– Can be used in the JDK
– Disallow same packages
– No versioning
 Accessibility
https://www.infoq.com/articles/java9-osgi-future-modularity/, https://www.infoq.com/articles/java9-osgi-future-modularity-
part-2/, https://www.baeldung.com/java-illegal-reflective-access, https://en.wikipedia.org/wiki/OSGi

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OSGi (Bundles)
 “[B]uild dependencies and
runtime dependencies can
and often do differ”
JPMS (Modules)
 “[T]he module system
should […] work [same] at
compile time, run time…”
Export-Package: org.example.foo;
version=1.0.1, org.example.bar;
version=2.1.0
Import-Package: org.example.foo;
version='[1,2)', org.example.bar;
version='[2.0,2.1)'
module A {
exports org.example.foo;
exports org.example.bar;
}
module B {
require A;
}
https://www.infoq.com/articles/java9-osgi-future-modularity/, https://www.infoq.com/articles/java9-osgi-future-modularity-
part-2/, https://www.baeldung.com/java-illegal-reflective-access, https://en.wikipedia.org/wiki/OSGi

137/360
JEP-213: Milling Project Coin
 From Java 7
– Allow @SafeVargs on private instance methods
– Allow effectively-final variables as resources in the try-
with-resources statement
– Allow diamond with anonymous classes in some cases
 From Java 8
– Remove underscore as legal identifier names
 In Java 9
– Support for private methods in interfaces

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 Nothing to mention, so much
work went into modularisation

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Collection Factory Methods
 No null values
 No modification
– Run-time exception
final List<String> list = List.of("Rick Deckard", "Roy Batty", "Harry Bryant", "Hannibal
Chew", "Gaff", "Holden", "Leon Kowalski", "Taffey Lewis", "Pris", "Rachael", "J.F.
Sebastian", "Dr. Eldon Tyrell", "Zhora", "Hodge", "Mary");
System.out.println(list);
list.add("Paul Atreides");
}
}

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Collection Factory Methods
 No null values
 No modification
– Run-time exception
final List<String> list = List.of("Rick Deckard", "Roy Batty", "Harry Bryant", "Hannibal
Chew", "Gaff", "Holden", "Leon Kowalski", "Taffey Lewis", "Pris", "Rachael", "J.F.
Sebastian", "Dr. Eldon Tyrell", "Zhora", "Hodge", "Mary");
System.out.println(list);
list.add("Paul Atreides");
}
}
[Rick Deckard, Roy Batty, Harry Bryant, [...] Tyrell, Zhora, Hodge, Mary]
Exception in thread "main" java.lang.UnsupportedOperationException
at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:142)
at [...]
at net.ptidej.newjava.collectionfactories.Example1.main(Example1.java:11)

143/360
JavaDB Removal
 JavaDB was a repackaging of Apache Derby
– Relational database
– Open-source
– Entirely in Java
– Embedded JDBC driver

144/360
JEP-254: Compact Strings
Problem and Solution
 More space-efficient
internal representation
– Not about using UTF-8
 From a UTF-16 char
array to a byte array
with an encoding flag
– ISO-8859-1/Latin-1 (1 byte
per char) or UTF-16 (2 bytes)
– String-related classes and
HotSpot intrinsic operations
Consequences
 Reduction in memory
footprint
 Substantial reductions of
GC activity
 Minor performance
regressions in some
corner cases

145/360
JEP-263: HiDPI Graphics
 Java programs sized and
rendered based on pixels
 HiDPI displays can have 2
to 3 times higher pixel
densities
 Windows Direct2D APIs
 Linux GTK+ 3 libraries
https://stackoverflow.com/questions/52519777/java-swing-app-looks-tiny-on-high-dpi-screen-when-it-should-be-scaled-to-normal

146/360
JEP-266: More on Concurrency
 “[A]synchronous stream processing with
non-blocking back pressure”
– https://www.reactive-streams.org/
https://www.baeldung.com/java-9-reactive-streams
// Given
final SubmissionPublisher<String> publisher = new SubmissionPublisher<>();
final EndSubscriber<String> subscriber = new EndSubscriber<>();
final List<String> items = List.of("1", "x", "2", "x", "3", "x");
// When
publisher.subscribe(subscriber);
items.forEach(publisher::submit);
publisher.close();
// Then
Awaitility.await().atMost(1000, TimeUnit.MILLISECONDS)
.until(() -> subscriber.consumedElements.containsAll(items));

147/360
JEP-268: XML Catalogs
 OASIS XML Catalogs standard, v1.1
– Map XML external identifiers into (local) URIs
 Java API
– javax.xml.catalog.*
<?xml version="1.0"?>
<!DOCTYPE catalog
PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
"http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd">
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog" prefer="public">
<public publicId="-//W3C//DTD XHTML 1.0 Strict//EN"
uri="dtd/xhtml1/xhtml1-strict.dtd"/>
<public publicId="-//W3C//DTD XHTML 1.0 Transitional//EN"
uri="dtd/xhtml1/xhtml1-transitional.dtd"/>
<public publicId="-//W3C//DTD XHTML 1.1//EN"
uri="dtd/xhtml11/xhtml11-flat.dtd"/>
</catalog>

150/360
JEP-282: jlink
 Assemble, optimize some modules and their
dependencies into a custom run-time image
– JEP-220: Modular run-time images
javac -d out module-info.java
javac -d out --module-path out
netptidejnewjavajlinkHelloWorld.java
jlink --module-path "%JAVA_HOME%jmods";out
--add-modules testJLinkModule
--output CustomJRE
cd CustomJRE/bib/
java --module testJLinkModule/net.ptidej.newjava.jlink.HelloWorld
https://www.baeldung.com/jlink

151/360
JEP-295: jaotc
 Ahead-of-time compilation
– Compile Java classes to native code
before launching the virtual machine
https://stackoverflow.com/questions/45298045/how-do-i-run-a-class-compiled-with-jaotc
javac Test.java
jaotc Test.class
jaotc --output libjava.base.so --module java.base
java -XX:AOTLibrary=./Test.so Test

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JEP-286: Local-variable Type
Inference
final List<String> list1 = new ArrayList<>();
System.out.println(list1);
final var list2 = new ArrayList<String>();
System.out.println(list2);
vs.

156/360
JEP-304: GC Interface
 “Improve the source code isolation of
different garbage collectors by introducing a
clean garbage collector (GC) interface.”
https://medium.com/@unmeshvjoshi/writing-your-own-garbage-collector-for-jdk12-8c83e3d0309b
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/gc/shared/collectedHeap.hpp#L90
class CollectedHeap : public CHeapObj<mtGC> {
virtual jint initialize() = 0;
virtual HeapWord* allocate_new_tlab(size_t min_size,
size_t requested_size,
size_t* actual_size) = 0;
virtual HeapWord* mem_allocate(size_t size,
bool* gc_overhead_limit_was_exceeded) = 0;
// ...

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JEP-307: Parallel Full GC
 Improve G1 worst-case with full parallel GC
– Before Java 9: Parallel GC
– Since Java 9: G1
https://dev.java/evolution/

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JEP-310: Application Class-Data
Sharing
 Improve startup and footprint
https://www.geeksforgeeks.org/class-data-sharing-in-java/
java -XX:+UnlockCommercialFeatures-XX:+UseAppCDS
-XX:DumpLoadedClassList=LoadedClasses.1st -jar AppCDS.jar
java -XX:+UnlockCommercialFeatures -Xshare:dump -XX:+UseAppCDS
-XX:SharedClassListFile=LoadedClasses.1st
-XX:SharedArchiveFile=CustomSharedArchive.jsa -cp AppCDS.jar
java -XX:UnlockCommercialFeatures -verbose -XShare:on
-XX:+UseAppCDS -XX:SharedArchiveFile=CUstomSharedArchive.jsa
-jar AppCDS.jar

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JEP-312: Thread-local Handshakes
 Callback on threads without performing a
global VM safepoint
 Possible and cheap to stop individual
threads and not just all threads
-XX:ThreadLocalHandshakes=<true|false>

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JEP-316: Heap Allocation on
Alternative Memory Devices
 Availability of cheap NVDIMM memory
– Non Volatile Dual In-line Memory Module
https://blog.workinghardinit.work/2019/07/18/a-quick-intro-to-nvdimm-n/
-XX:AllocateHeapAt=<path>

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JEP-317: Experimental Java-based
JIT Compiler
 Efficient JIT compiler
for Java in Java
 As of 18/09/30
https://www.graalvm.org/
https://www.javacodegeeks.com/2018/10/java-graalvm-database-stream-performance.html
-XX:+UnlockExperimentalVMOptions
-XX:+UseJVMCICompiler

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JEP-314: Additional Unicode
Language-Tag Extensions
 BCP 47 language tags
– Codes to identify languages
• en: English
• en-US: English, in United States
• km-Khmr-KH: Khmer, in Khmer script, in Cambodia
• km-fonipa: Khmer, transcribed in IPA
 Changes to many APIs
– java.text.DateFormat, java.util.Currency,
java.time.format.DateTimeFormatter, …
https://help.keyman.com/developer/current-version/reference/bcp-47

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JEP-296: Consolidated JDK Forest
 Until Java 9
– Eight repos: root, corba, hotspot, jaxp, jaxws,
jdk, langtools, and nashorn
 Since Java 10
– One unified repository
$ROOT/jdk/src/java.base
...
$ROOT/langtools/src/java.compiler
...

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JEP-296: Consolidated JDK Forest
 Until Java 9
– Eight repos: root, corba, hotspot, jaxp, jaxws,
jdk, langtools, and nashorn
 Since Java 10
– One unified repository
$ROOT/jdk/src/java.base
...
$ROOT/langtools/src/java.compiler
...
$ROOT/src/java.base
$ROOT/src/java.compiler
...

167/360
JEP-313: Native-Header Generation
Tool Removal
 javah features (and more) now in javac
javac HelloWorld.java
javah HelloWorld
javac -h jni -d bin HelloWorld.java
vs.

168/360
JEP-319: Root Certificates
 Default set of root Certification Authority
(CA) certificates
– Oracle Java SE Root CA becomes open source
– OpenJDK can use the same certificates

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JEP-322: Time-based Release
Versioning
 New version scheme
final Version version = Runtime.version();
System.out.println(version);
System.out.print("Feature: ");
System.out.println(version.feature());
System.out.print("Interim: ");
System.out.println(version.interim());
System.out.print("Update: ");
System.out.println(version.update());
System.out.print("Patch: ");
System.out.println(version.patch());
System.out.print("Build: ");
System.out.println(version.build());
System.out.print("Optional: ");
System.out.println(version.optional());
System.out.print("Pre: ");
System.out.println(version.pre());

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JEP-322: Time-based Release
Versioning
 New version scheme
final Version version = Runtime.version();
System.out.println(version);
System.out.print("Feature: ");
System.out.println(version.feature());
System.out.print("Interim: ");
System.out.println(version.interim());
System.out.print("Update: ");
System.out.println(version.update());
System.out.print("Patch: ");
System.out.println(version.patch());
System.out.print("Build: ");
System.out.println(version.build());
System.out.print("Optional: ");
System.out.println(version.optional());
System.out.print("Pre: ");
System.out.println(version.pre());
21.0.1+12-LTS-29
Feature: 21
Interim: 0
Update: 1
Patch: 0
Build: Optional[12]
Optional: Optional[LTS-29]
Pre: Optional.empty

173/360
JEP-181: Nest-based Access Control
 Before Java 11
– Bridge method, e.g.,
access$000(Example1)
 Since Java 11
– Direct access
– Access to nest mates’
private members
https://mkyong.com/java/java-11-nest-based-access-control/
private String name = "I'm Example1!";
public class A {
public void printName() {
}
}
public class B {
System.out.println(Example1.this.name);
}
public class B1 {
}
}
}
final Example1 e1 = new Example1();
final Example1.B b = e1.new B();
final Example1.B.B1 b1 = b.new B1();
b1.printName();
}
}

174/360
public class A {
}
}
public class B {
}
public class B1 {
}
}
}
System.out.println(A.class.getNestHost());
System.out.println(A.class.isNestmateOf(B.class));
for (final Class<?> clazz : Example2.B.class.getNestMembers()) {
System.out.println(clazz);
}
}
}

175/360
public class A {
}
}
public class B {
}
public class B1 {
}
}
}
System.out.println(A.class.getNestHost());
System.out.println(A.class.isNestmateOf(B.class));
for (final Class<?> clazz : Example2.B.class.getNestMembers()) {
System.out.println(clazz);
}
}
}
class net.ptidej.newjava.nest.Example2
true
class net.ptidej.newjava.nest.Example2
class net.ptidej.newjava.nest.Example2$A
class net.ptidej.newjava.nest.Example2$B
class net.ptidej.newjava.nest.Example2$B$B1

176/360
JEP-323: Local-variable Syntax for
Lambda Parameters
interface Comparator<T> {
int compare(final T a, final T b);
}
final Comparator<String> comparator1 = new Comparator<>() {
@Override
public int compare(final String a, final String b) {
return a.compareTo(b);
}
};
System.out.println(comparator1.compare("Hello", "World"));
final Comparator<String> comparator2 = (a, b) -> a.compareTo(b);
final Comparator<String> comparator3 = (String a, String b) -> a.compareTo(b);
final Comparator<String> comparator4 = (final var a, final var b) -> a.compareTo(b);
final Comparator<String> comparator5 = (@NonNull var a, @NonNull var b) -> a.compareTo(b);
}
}

177/360
JEP-323: Local-variable Syntax for
Lambda Parameters
interface Comparator<T> {
int compare(final T a, final T b);
}
final Comparator<String> comparator1 = new Comparator<>() {
@Override
public int compare(final String a, final String b) {
return a.compareTo(b);
}
};
final Comparator<String> comparator2 = (a, b) -> a.compareTo(b);
final Comparator<String> comparator3 = (String a, String b) -> a.compareTo(b);
final Comparator<String> comparator4 = (final var a, final var b) -> a.compareTo(b);
final Comparator<String> comparator5 = (@NonNull var a, @NonNull var b) -> a.compareTo(b);
}
}
Now posssible

179/360
JEP-309: Dynamic .class Constants
 Extend the class-file format with a new
constant-pool form
– CONSTANT_Dynamic
 Avoid initialising “expansive” values
– Also, no need to use volatile
https://www.javacodegeeks.com/2018/08/hands-on-java-constantdynamic.html

180/360
Problem: How to share some “expensive” data
among different threads?
Solution: Singleton design pattern
public class SomeExpensiveData {
public SomeExpensiveData() {
// Some very expensive (time, space) data to create
System.out.println("tSomeExpensiveData instance created");
}
}

181/360
public class MyCallable implements Callable<SomeExpensiveData> {
private static MyCallable UniqueInstance;
public static MyCallable getInstance() {
if (MyCallable.UniqueInstance == null) {
synchronized (MyCallable.class) {
MyCallable.UniqueInstance = new MyCallable();
}
}
}
return MyCallable.UniqueInstance;
}
private volatile SomeExpensiveData someExpensiveData;
private MyCallable() {
this.someExpensiveData = new SomeExpensiveData();
}
@Override
public SomeExpensiveData call() throws Exception {
return this.someExpensiveData;
}
}

182/360
}
}
}
}
}
@Override
}
}
Not a true constant
No caching, etc.

183/360
}
}
}
}
}
@Override
}
}
Not a true constant
No caching, etc.
Eager initialisation

184/360
 Dynamic constants
– Created once at run-time
– Can be shared among threads
– Can be cached, optimised, etc.
Problem: How to create dynamically a constant
Solution: CONSTANT_Dynamic

185/360
 Dynamic constants, javac vs. java
– Cannot be created from source code
• As of 24/03/24
– Can be created in the byte code
 Byte code generation, manipulation library
– Create, modify Java classes at run-time

186/360
final Unloaded<Callable> unloaded = new ByteBuddy().subclass(Callable.class)
.method(ElementMatchers.named("call")).intercept(FixedValue.value(
JavaConstant.Dynamic.ofInvocation(SomeExpensiveData.class.getConstructor()))).make();
final Constructor<? extends Callable> loaded =
unloaded.load(Example2.class.getClassLoader()).getLoaded().getConstructor();
final Callable<SomeExpensiveData> first = loaded.newInstance();
final Callable<SomeExpensiveData> second = loaded.newInstance();
System.out.println("tCallable instances created");
assertThat(first.call()).isEqualTo(second.call());

187/360
test_CONSTANT_Dynamic()
Callable instances created
SomeExpensiveData instance created

188/360
Lazy initialisation: two
instances created, but not
SomExpensiveData

189/360
Lazy initialisation: two
instances created, but not
SomExpensiveData
SomExpensiveData created
only once, with first call()

190/360
// (version 17 : 61.0, super bit)
public class net.bytebuddy.[...].Callable$ByteBuddy$7xbn1EIQ implements java.util.concurrent.Callable
public java.lang.Object call() throws java.lang.Exception;
0 ldc <Dynamic> 0 _ net.ptidej.newjava.constantdynamic.SomeExpensiveData [28]
2 areturn
public Callable$ByteBuddy$7xbn1EIQ();
0 aload_0 [this]
1 invokespecial java.lang.Object() [29]
4 return
Bootstrap methods:
0 : # 24 invokestatic java/lang/invoke/ConstantBootstraps.invoke:([...])Ljava/lang/Object;
Method arguments:
#17 net/ptidej/newjava/constantdynamic/SomeExpensiveData.<init>:()V

191/360
// (version 17 : 61.0, super bit)
public class net.bytebuddy.[...].Callable$ByteBuddy$7xbn1EIQ implements java.util.concurrent.Callable
public java.lang.Object call() throws java.lang.Exception;
0 ldc <Dynamic> 0 _ net.ptidej.newjava.constantdynamic.SomeExpensiveData [28]
2 areturn
public Callable$ByteBuddy$7xbn1EIQ();
0 aload_0 [this]
1 invokespecial java.lang.Object() [29]
4 return
Bootstrap methods:
0 : # 24 invokestatic java/lang/invoke/ConstantBootstraps.invoke:([...])Ljava/lang/Object;
Method arguments:
#17 net/ptidej/newjava/constantdynamic/SomeExpensiveData.<init>:()V
CONSTANT_Dynamic
with bootstrap method

192/360
JEP-331: Low-overhead Heap
Profiling
 Since Java 6
– No more JVM Profiler
Interface (JVMPI)
– No more JVM Debug
Interface (JVMDI)
– Replaced by JVM Tool
Interface (JVMTI)
 Sampling of Java heap
allocations
– All allocations
– Low-overhead
– Well-defined API
– Live, dead objects
https://docs.oracle.com/en/java/javase/11/docs/specs/jvmti.html

193/360
JEP-331: Low-overhead Heap
Profiling
https://docs.dynatrace.com/docs/platform-modules/applications-and-microservices/profiling-and-optimization/memory-profiling

194/360
JEP-333: Scalable Low-latency GC
 Z Garbage Collector
– GC pause no more than 10ms
– Handle megabyte to terabyte heaps
– No more than 15% throughput reduction wrt. G1
– Foundation for future features and optimisations
– (Only on 64bit operating systems)
-XX:+UnlockExperimentalVMOptions -XX:+UseZGC

196/360
JEP-320: Java EE and CORBA
Modules Removal
 Since Java 1.2
– OMG CORBA API
– ORB implementation
– CosNaming implementation
– idlj compiler
– Support for IDL and IIOP in rmic compiler
– No significant interest in CORBA anymore
 Since Java 6
– Full Web Services stack
– Now available from third parties
 Deprecated in Java 9

197/360
JEP-321: HTTP Client
 Problems with HttpURLConnection API
– Designed for (now dead) protocols (gopher…)
– Designed before HTTP/1.1
– Too abstract
– Hard to use
– Badly documented
– Blocking mode only
– Very hard maintenance

198/360
JEP-321: HTTP Client
 Three core classes
– HttpClient as a container for configuration
information common to multiple requests
– HttpRequest for requests sent by HttpClient
– HttpResponse for the result of an HttpRequest
https://www.baeldung.com/java-9-http-client

199/360
JEP-321:
final HttpRequest request = HttpRequest.newBuilder()
.uri(new URI("https://postman-echo.com/get"))
.version(HttpClient.Version.HTTP_2)
.timeout(Duration.ofSeconds(10))
.header("key1", "value1")
.GET()
.build();
final HttpClient client = HttpClient.newHttpClient();
final HttpResponse<String> response = client.send(request,
HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());

200/360
JEP-321:
final HttpRequest request = HttpRequest.newBuilder()
.uri(new URI("https://postman-echo.com/get"))
.version(HttpClient.Version.HTTP_2)
.timeout(Duration.ofSeconds(10))
.GET()
.build();
final HttpClient client = HttpClient.newHttpClient();
final HttpResponse<String> response = client.send(request,
HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());
{
"args": {},
"headers": {
"x-forwarded-proto": "https",
"x-forwarded-port": "443",
"host": "postman-echo.com",
"x-amzn-trace-id": "Root=1-660163f4-038cfd7075f93fad1e79f19e",
"key1": "value1",
"key2": "value2",
"user-agent": "Java-http-client/21.0.1"
},
"url": "https://postman-echo.com/get"
}

201/360
JEP-327: Unicode 10
 Major version of the Unicode Standard
 Support
– Character and String in java.lang
– NumericShaper in java.awt.font
– Bidi, BreakIterator, Normalizer in java.text

202/360
JEP-335: Nashorn Deprecation
 Since Java 8
– JEP-174
 ECMAScript changes rapidly
– Language
– APIs
 Maintenance challenges
– Deprecate Nashorn, its APIs, and jjs

204/360
JEP-328: Flight Recorder
 Monitoring tool
– Collects information about the events in a JVM
– An event
• Name
• Timestamp
• Other data
– Thread data, state of the heap, etc.
https://www.baeldung.com/java-flight-recorder-monitoring
-XX:+UnlockCommercialFeatures
-XX:+FlightRecorder
-XX:StartFlightRecording=duration=200s,filename=flight.jfr

205/360
JEP-328: Flight Recorder
https://www.baeldung.com/java-flight-recorder-monitoring

206/360
JEP-330: Single-file Source-code
Programs Launching
 Lower the (early) learning curve
– But no dependency management
java –cp some.jar HelloWorld.java

207/360
JEP-336: Pack200 Tools and API
Deprecation
 Since Java 5
– Compression scheme for JAR files
– To accommodate 56k modems
 Since Java 9 (and JEP-220)
– Modules
– Compression
– No more applets
– Maintenance challenges
– Modularisation challenges

210/360
 Nothing to mention?

212/360
JEP-344: Abortable Mixed
Collections
 Ability for G1 to abort its collection pauses
 G1 predicts the number of regions to collect
and proceeds only with abortable ones
 Lower pause latency and higher probability
to achieve pause-time target
https://blogs.oracle.com/javamagazine/post/understanding-the-jdks-new-superfast-garbage-collectors
-XX:G1MixedGCCountTarget=<number of mixed garbage collections>

213/360
JEP-346: Unused Committed
Memory Prompt Return
 G1 automatically returns heap memory to
the operating system when idle
-XX:G1PeriodicGCInterval=<true|false>
-XX:G1PeriodicGCInvokesConcurrent=<true|false>
-XX:G1PeriodicGCSystemLoadThreshold=<average 1-minute system load>

215/360
JEP-334: JVM Constants API
 API to describes some class-file and run-
time elements (e.g., constants)
https://iampravo.medium.com/java-12-features-and-highlights-81938474cd31
final ClassDesc example1ClassDesc = ClassDesc.of("[...].constantsapi", "Example1");
final MethodTypeDesc mainMethodTypeDesc = MethodTypeDesc.of(example1ClassDesc);
final MethodHandleDesc mainMethodHandleDesc = MethodHandleDesc.ofMethod(
DirectMethodHandleDesc.Kind.STATIC, example1ClassDesc, "main", mainMethodTypeDesc);
System.out.println("Class descriptor: " + example1ClassDesc);
System.out.println("Method type descriptor: " + mainMethodTypeDesc);
System.out.println("Method handle descriptor: " + mainMethodHandleDesc);
}
}

216/360
JEP-334: JVM Constants API
 API to describes some class-file and run-
time elements (e.g., constants)
https://iampravo.medium.com/java-12-features-and-highlights-81938474cd31
final ClassDesc example1ClassDesc = ClassDesc.of("[...].constantsapi", "Example1");
final MethodTypeDesc mainMethodTypeDesc = MethodTypeDesc.of(example1ClassDesc);
final MethodHandleDesc mainMethodHandleDesc = MethodHandleDesc.ofMethod(
DirectMethodHandleDesc.Kind.STATIC, example1ClassDesc, "main", mainMethodTypeDesc);
System.out.println("Class descriptor: " + example1ClassDesc);
System.out.println("Method type descriptor: " + mainMethodTypeDesc);
System.out.println("Method handle descriptor: " + mainMethodHandleDesc);
}
}
Class descriptor: ClassDesc[Example1]
Method type descriptor: MethodTypeDesc[()Example1]
Method handle descriptor: MethodHandleDesc[STATIC/Example1::main()Example1]

218/360
JEP-230: Microbenchmark Suite
 Java Microbenchmark Harness (JMH)
– An annotation-based DSL
• @State, @Fork, @Warmup, @Measurement, @Benchmark…
 Microbenchmarks suite integrated into
OpenJDK source code
https://cl4es.github.io/2018/11/16/JEP-230-Microbenchmarks-Suite.html
make build-microbenchmark

219/360
 Java Microbenchmark Harness (JMH)
– An annotation-based DSL
• @State, @Fork, @Warmup, @Measurement, @Benchmark…
 Microbenchmarks suite integrated into
OpenJDK source code
https://cl4es.github.io/2018/11/16/JEP-230-Microbenchmarks-Suite.html
make build-microbenchmark
build/$PROFILE/images/test/micro/benchmarks.jar

220/360
 Run one java.util.UUIDBench benchmark
– https://github.com/openjdk/jdk/blob/master/test/mi
cro/org/openjdk/bench/java/util/UUIDBench.java
https://cl4es.github.io/2021/01/04/Investigating-MD5-Overheads.html
make test TEST=micro:UUIDBench.fromType3Bytes

221/360
 Run one java.util.UUIDBench benchmark
– https://github.com/openjdk/jdk/blob/master/test/mi
cro/org/openjdk/bench/java/util/UUIDBench.java
https://cl4es.github.io/2021/01/04/Investigating-MD5-Overheads.html
make test TEST=micro:UUIDBench.fromType3Bytes
Benchmark Score Error Units
fromType3Bytes 1.460 ± 0.089 ops/us

222/360
 Benchmarking the
JVM is difficult
– Just-in-time compiler
– Dead code elimination
– Loop unrolling
– Method inlining
– …
– Warmup iterations
– Iteration durations
– …
https://www.oracle.com/technical-resources/articles/java/architect-benchmarking.html

223/360
Java 13
2019/09/17
2019/09/17
2019/09/17
2019/09/17

225/360

227/360
JEP-351: Unused Memory
Uncommit
 ZGC automatically returns heap memory to
the operating system when idle
– Cf. JEP-346
-XX:ZUncommitDelay=<seconds>

229/360
JEP-353: Legacy Socket API
Reimplementation
 Reimplementations
– java.net.Socket
– java.net.ServerSocket
 Simpler, modern
 Easier to maintain, debug
 Ready for user-mode threads
– Fibers, Project Loom

231/360

234/360
-XX:+ShowCodeDetailsInExceptionMessages
JEP-358: Helpful
NullPointerExceptions
 Describe precisely which variable was null
class Employee {
String getName() {
// return "Bob";
return null;
}
}
final Employee e = new Employee();
e.getName().toString();
}
}

235/360
JEP-358: Helpful
class Employee {
String getName() {
// return "Bob";
return null;
}
}
}
}
Exception in thread "main" java.lang.NullPointerException
at net.ptidej.newjava.helpfulnullpointerexceptions.Example1.main(Example1.java:13)

236/360
JEP-358: Helpful
class Employee {
String getName() {
// return "Bob";
return null;
}
}
}
}
Exception in thread "main" java.lang.NullPointerException
Exception in thread "main" java.lang.NullPointerException: Cannot invoke
"String.toString()" because the return value of "[...].Employee.getName()" is null

237/360
JEP-361: switch Expressions
https://medium.com/@imagarg/switch-expression-jep-361-3b5649ec36c9
private static int getDayLength(final Day day) {
int numberOfCharacters = 0;
switch (day) {
case MONDAY:
case FRIDAY:
case SUNDAY:
numberOfCharacters = 6;
break;
case TUESDAY:
break;
case THURSDAY:
case SATURDAY:
break;
case WEDNESDAY:
break;
default:
throw new IllegalArgumentException();
}
return numberOfCharacters;
}
private static int getDayLength(final Day day) {
int result = switch (day) {
case MONDAY, FRIDAY, SUNDAY -> 6;
case TUESDAY -> 7;
case THURSDAY, SATURDAY -> 8;
case WEDNESDAY -> 9;
default ->
throw new IllegalArgumentException();
};
return result;
}
enum Day {
MONDAY, TUESDAY,
WEDNESDAY,
THURSDAY, FRIDAY,
SATURDAY, SUNDAY;
}

239/360
JEP-345: NUMA-Aware Memory
Allocation
 NUMA-aware memory
allocation to increase
G1 performance
– Non-uniform memory
access
– Multi-socket computers
• E.g., HP Z820
-XX:UseParallelGC=<true|false>

240/360
JEP-345: NUMA-Aware Memory
Allocation
 NUMA-aware memory
allocation to increase
G1 performance
– Non-uniform memory
access
– Multi-socket computers
• E.g., HP Z820
-XX:UseParallelGC=<true|false>
Two CPUs, with
their own DIMMs

Evolution and Examples of Java Features, from Java 1.7 to Java 22

Evolution and Examples of Java Features, from Java 1.7 to Java 22

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