Java 15 - Updates

A presentation about the updates introduced in Java 15.

Text Blocks, Pattern Matching for instanceof, Foreign Memory Access APIs, Sealed Classes, Records and Goodbye Nashorn.

Transcript

1. sbordet@webtide.com Java 15 - Updates @simonebordet
2. sbordet@webtide.com Simone Bordet • @simonebordet • sbordet@webtide.com • Java Champion • Works @ Webtide • The company behind Jetty and CometD
3. sbordet@webtide.com Java 15 Confirmed Features
4. sbordet@webtide.com Text Blocks
5. sbordet@webtide.com Java 15 - Text Blocks • Text Blocks String json = """ __{"o": "JUG Torino", __"y": 2001 __}"""; => "{\"o\": \"JUG Torino\",\n\"y\": 2001\n}"
6. sbordet@webtide.com • Margin Management String json = """ ____{ _____"o": "JUG Torino", _____"y": 2001 ____} ___"""; => "_{__\"o\": \"JUG Torino\",\n__\"y\": 2001\n_}\n" Java 15 - Text Blocks
7. sbordet@webtide.com Java 15 - Text Blocks • Special Cases String empty = """ """; String error = """{ }"""; Error: illegal text block open delimiter sequence
8. sbordet@webtide.com Java 15 - Text Blocks • Special Cases ◦ \s => inserts space ◦ \ => removes newline String sql = """ select *\s\ from users; """; => "select * from users;\n"
9. sbordet@webtide.com Java 15 - Text Blocks • Concatenation String ohNo = """ { "id": \"""" + id + """ // cannot put dquote here ", "role": "admin" // must zero the indentation }"""; String phew = """ { "id": "${id}", "role": "admin" }""".replace("${id}", id);
10. sbordet@webtide.com Java 15 Second Previews
11. sbordet@webtide.com Pattern Matching for instanceof
12. sbordet@webtide.com Java 15 - Pattern Matching • Pattern Matching for instanceof boolean equals(Object obj) { if (obj instanceof MyClass that) { return this.field.equals(that.field); } return false; }
13. sbordet@webtide.com Records
14. sbordet@webtide.com Java 15 - Records • Records • Records are immutable, final, data holder classes ◦ Typed tuples • Automatic constructor and getters ◦ Plus equals(), hashCode(), toString() public record MinMax(int min, int max) {}
15. sbordet@webtide.com Java 15 - Records • Usage ◦ int m = minMax.max; // field access ◦ int m = minMax.max(); // getter access ◦ IntSupplier s = minMax::max; // getter access • Records can be customized ◦ Custom constructors ◦ Override equals(), hashCode() and toString() ◦ Add methods (both static and virtual) ◦ Fields cannot be named hashCode, toString, wait...
16. sbordet@webtide.com Java 15 - Records public record MinMax(int min, int max) { public MinMax { // compact constructor if (min > max) throw new IllegalArgumentException(); } public MinMax(Histogram h) { // custom constructor this(h.min, h.max); } public static MinMax zero() { return new MinMax(0, 0); } public int avg() { return (min + max) / 2; } // warning: hides getter! don’t do it! public int max() { return 0; } }
17. sbordet@webtide.com Java 15 - Records • Use cases for Records • Multiple return values ◦ MinMax minMax(int[] array) { ... } ◦ MinMax is more expressive than Pair<int, int> • DTOs ◦ But not JPA entities (mutable)
18. sbordet@webtide.com Java 15 - Records • Temporary tuples: private static String longest(Stream<String> stream) { // Method-local record class. record StrLen(String s, int l) {} return stream.map(s -> new StrLen(s, s.length())) .max(Comparator.comparingInt(StrLen::l)) .map(sl -> sl.s) .orElse(null); }
19. sbordet@webtide.com Java 15 - Records • Records & Pattern Matching • 1-1 relationship between data and class ◦ Easy to deconstruct a record, recursively record Pctl(int p50, int p90, int p95, int p99) {} record Stats(Pctl percentile, MinMax minMax) {}
20. sbordet@webtide.com Java 15 - Records • Records & Value Types • Value Types => flat and dense object layout in memory ◦ But must give up identity and nullability • Records => data tuple and deconstruction ◦ But must give up extension, hiding and mutability • May need both at the same time
21. sbordet@webtide.com Foreign Memory Access
22. sbordet@webtide.com Java 15 - Foreign Memory Access • Foreign Memory Access API (second incubation) • MemorySegment ◦ A contiguous region of memory (spatially bounded) ◦ Explicitly deallocated (temporally bounded) • MemoryLayout ◦ A (named) description of a memory segment • Finally, struct and union in Java!
23. sbordet@webtide.com Java 15 - Foreign Memory Access WARNING! C code! struct { double x; double y; } complex[128]; x y x y x y 0 1 2
24. sbordet@webtide.com Java code class Complex { double x; double y; } var cxs = new Complex[128]; Java 15 - Foreign Memory Access WARNING! C code! struct { double x; double y; } complex[128]; x y x y x y 0 1 2 3 4 5 x hdr x y hdr y x hdr y 0 1 2
25. sbordet@webtide.com Java 15 - Foreign Memory Access WARNING! C code! struct { double x; double y; } complex[128];
26. sbordet@webtide.com Java code // 64-bit double var real = MemoryLayout.ofValueBits(64, ByteOrder.BIG_ENDIAN); var complex = MemoryLayout.ofStruct( real.withName("x"), real.withName("y") ); var shape = MemoryLayout.ofSequence(128, complex); Java 15 - Foreign Memory Access WARNING! C code! struct { double x; double y; } complex[128];
27. sbordet@webtide.com Java 15 - Foreign Memory Access • Unions in Java // A real number in 64 bits. ValueLayout real = MemoryLayout.ofValueBits(64, ByteOrder.BIG_ENDIAN); // Struct. GroupLayout complex = MemoryLayout.ofStruct(real.withName("x"), real.withName("y")); GroupLayout polar = MemoryLayout.ofStruct(real.withName("rho"), real.withName("theta")); // Union. GroupLayout coords = MemoryLayout.ofUnion(complex.withName("complex"), polar.withName("polar"));
28. sbordet@webtide.com Java 15 - Foreign Memory Access // A shape in a game. SequenceLayout shape = MemoryLayout.ofSequence(3, complex); var ys = shape.varHandle(long.class, PathElement.sequenceElement(), PathElement.groupElement("y")); ys.set(shape.baseAddress(), 1L, 13L); x y x y x y x y x 13 x y
29. sbordet@webtide.com Java 15 - Foreign Memory Access // Use try-with-resources to close the segment. try (MemorySegment segment = MemorySegment.allocateNative(shape)) { // Translate the shape on the y axis. for (long i = 0; i < shape.elementCount().orElse(0); ++i) { // Get the current y coordinate. long y = (Long)ys.get(segment.baseAddress(), i); // Set the new y coordinate. ys.set(segment.baseAddress(), i, y + 1); } }
30. sbordet@webtide.com Java 15 First Preview
31. sbordet@webtide.com Sealed Classes
32. sbordet@webtide.com Java 15 - Sealed Classes sealed interface Celestial permits Star, Planet, Satellite {}
33. sbordet@webtide.com Java 15 - Sealed Classes sealed interface Celestial permits Star, Planet, Satellite {} final class Planet implements Celestial {}
34. sbordet@webtide.com Java 15 - Sealed Classes sealed interface Celestial permits Star, Planet, Satellite {} final class Planet implements Celestial {} non-sealed class Star implements Celestial {}
35. sbordet@webtide.com Java 15 - Sealed Classes sealed interface Celestial permits Star, Planet, Satellite {} final class Planet implements Celestial {} non-sealed class Star implements Celestial {} sealed class Satellite implements Celestial permits Satellite.Natural, Satellite.Artificial { final class Artificial extends Satellite {} final class Natural extends Satellite {} }
36. sbordet@webtide.com Java 15 - Sealed Classes sealed class Shape permits Circle, Rectangle {} • How do you implement Shape.getArea()?
37. sbordet@webtide.com Java 15 - Sealed Classes sealed class Shape permits Circle, Rectangle { abstract double getArea(); } record Circle(double r) implements Shape { @Override double getArea() { return Math.PI * r * r; } }
38. sbordet@webtide.com Java 15 - Sealed Classes sealed class Shape permits Circle, Rectangle { double getArea() { // Enhanced switch from Java 16. return switch (this) { case Circle(double r) -> Math.PI * r * r; case Rectangle(double h, double w) -> h * w; } } }
39. sbordet@webtide.com Java 15 - Sealed Classes • Sealed Classes & Records sealed interface Expr permits AddExpr, ConstExpr, ... {} record ConstExpr(int value) implements Expr {} record AddExpr(Expr a, Expr b) implements Expr {} // Enhanced switch from Java 16. static int eval(Expr expr) { return switch (expr) { case ConstExpr(int v) -> v; case AddExpr(Expr lt, Expr rt) -> eval(lt) + eval(rt); ... }
40. sbordet@webtide.com Java 15 - Sealed Classes • Use sealed classes to restrict implementations • enum -> same implementation, different values • sealed -> different implementations • Use sealed & records for simple and known domains ◦ sealed class Optional permits None, Some {}
41. sbordet@webtide.com Java 15 Other Features
42. sbordet@webtide.com Java 15 - Other Updates • Additions ◦ JEP 371: Hidden Classes ◦ JEP 373: Reimplement the Legacy DatagramSocket API ◦ JEP 377: ZGC: A Scalable Low-Latency Garbage Collector ◦ JEP 379: Shenandoah: A Low-Pause-Time Garbage Collector • Deprecations ◦ JEP 374: Disable and Deprecate Biased Locking ◦ JEP 385: Deprecate RMI Activation for Removal • Removals ◦ JEP 381: Remove the Solaris and SPARC Ports ◦ JEP 372: Remove the Nashorn JavaScript Engine
43. sbordet@webtide.com Conclusions
44. sbordet@webtide.com Java 15 - Conclusions • Text Blocks • Sealed Classes, Records & Pattern matching ◦ Still in preview • Foreign Memory Access ◦ For hard-core data structures • Goodbye Nashorn • Goodbye Solaris & SPARC
45. sbordet@webtide.com Java 15 - Updates • References • https://jdk.java.net/15/release-notes • New Features • Removed Features • Deprecated Features • API Differences with Java 14
46. sbordet@webtide.com Questions?