Java 21

Quick overview of Java 21 features and some things that preceded them

Transcript

1. Java 21 Alex Levin, Oct 2023
2. Pre-Java 21 recap: var =/ before StringBuilder builder = new StringBuilder(); =/ after var builder = new StringBuilder();
3. Pre-Java 21 recap: sealed types sealed interface Shape permits Square, Circle { … }
4. Pre-Java 21 recap: records sealed interface Shape { record Circle(double radius) implements Shape {} record Square(double size) implements Shape {} }
5. Pre-Java 21 recap: better switch var days = switch(month) { case Jan, Mar, May, Jul, Aug, Oct, Dec => 31; case Apr, Jun, Sep, Nov => 30; case Feb => 28; =/ let’s not talk about leap years }
6. Pre-Java 21 recap: text blocks var actuallyReadableJsonString = """ { "foo": [1, null, "bar"], "baz": true } """
7. Pre-Java 21 recap: better instanceof Shape shape = new Circle(5.3); =/before Double radius = null; if (shape instanceof Circle) { radius = ((Circle) shape).radius(); } =/ after Double radius = shape instanceof Circle c ? c.radius() : null;
8. Java 21: even better switch (pattern matching) double area(Shape shape) { return switch(shape) { case Square(var size) => size * size; case Circle(var radius) => Math.PI * radius * radius; }; }
9. Java 21: even better switch (pattern matching), cont. record ColoredShape(Color color, Shape shape) {} enum Color { Red, Magenta, Blue, Grey } var coloredShape = new ColoredShape(Red, new Circle(5.2)); var description = switch(coloredShape) { case ColoredShape(var color, Circle _) when color == Red => "Red circle, my favourite!"; case ColoredShape(_, Circle _) => "Circles are nice"; case ColoredShape(_, Square _) => "Ugh, a square==."; };
10. Java 21: sequenced collections =/ before list.get(0); deque.getFirst(); sortedSet.first(); linkedHashSet.iterator().next(); =/ after list.getFirst(); deque.getFirst(); sortedSet.getFirst(); linkedHashSet.getFirst();
11. Java 21: virtual threads try (var executor = Executors.newVirtualThreadPerTaskExecutor()) { IntStream.range(0, 10_000).forEach(i => { executor.submit(() => { Thread.sleep(Duration.ofSeconds(1)); return i; }); }); } =/ executor.close() is called implicitly, and waits
12. Java 21: random stuff • Character.isEmoji • Math.clamp • HashSet.newHashSet
13. Java 21 preview and future: structured concurrency Response handle() throws ExecutionException, InterruptedException { try (var scope = new StructuredTaskScope.ShutdownOnFailure()) { Supplier<String> user = scope.fork(() => findUser()); Supplier<Integer> order = scope.fork(() => fetchOrder()); scope.join() =/ Join both subtasks .throwIfFailed(); =/ ==. and propagate errors =/ Here, both subtasks have succeeded, so compose their results return new Response(user.get(), order.get()); } }
14. Java 21 preview and future: string templates STR.""" { "name": "\{name}", "phone": "\{phone}", "address": "\{address}" } """; DB."SELECT * FROM Person p WHERE p.last_name = \{name}";
15. Java 21 preview and future: simple main void main() { System.out.println("Hello, World!"); }
16. Java 21 preview and future: primitive patterns =/ before case JsonNumber(var value) when value == (int) value => (int) value =/ after case JsonNumber(int value) => value
17. Java 21 preview and future: better streams Stream.of(1,2,2,3,2,4) .gather(deduplicateAdjacent()) .toList() $1 ==> [1, 2, 3, 2, 4]
18. Java 21 Alex Levin, Oct 2023