Add jdk28-preview module: JDK 28 early-access build, value classes, strict init flag, PEM, JSON incubator

Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01Gth99spB1CzQmBFofXmU4Z
2026-09-28 08:48:04 +00:00
parent 57a04dc393
commit c8ff3acf09
15 changed files with 221 additions and 0 deletions
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+# 00-environment
+--- JDK 28 early-access:
+openjdk version "28-ea" 2027-03-23
+OpenJDK 64-Bit Server VM (build 28-ea+17-1282, mixed mode, sharing)
+--- JDK 25:
+openjdk version "25.0.4.1" 2026-08-18 LTS
+OpenJDK 64-Bit Server VM Temurin-25.0.4.1+1 (build 25.0.4.1+1-LTS, mixed mode, sharing)
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+# 01-value-classes: ValueClasses.java on JDK 28 with --enable-preview
+p == q: true, equals: true
+isValue: true
+synchronized on a value object: java.lang.IdentityException: Cannot synchronize on an instance of value class ValueClasses$Point
+--- IntegerIdentity.java: same source, three runs
+JDK 25:                 Integer 1000 == Integer 1000: false
+JDK 28, no preview:     Integer 1000 == Integer 1000: false
+JDK 28, --enable-preview: Integer 1000 == Integer 1000: true
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+# 02-forgot-the-preview-flag
+--- javac ValueClasses.java (no --enable-preview):
+src/ValueClasses.java:3: error: value classes are a preview feature and are disabled by default.
+	value record Point(int x, int y) {}
+	^
+  (use --enable-preview to enable value classes)
+--- java ValueClasses (compiled with the flag, run without):
+Error: LinkageError occurred while loading main class ValueClasses
+	java.lang.UnsupportedClassVersionError: Preview features are not enabled for ValueClasses (class file version 72.65535). Try running with '--enable-preview'
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+# 03-strict-init-flags (javap -v -p, field flags only)
+--- StrictFieldProbe$Money
+  final long cents;
+    flags: (0x0810) ACC_FINAL, ACC_STRICT_INIT
+--- StrictFieldProbe$Legacy
+  final long cents;
+    flags: (0x0010) ACC_FINAL
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+# 04-pem-encodings (JEP 542): PemRoundTrip.java
+--- JDK 28, no flags:
+-----BEGIN PUBLIC KEY-----
+round trip equal: true
+--- JDK 25, no flags:
+src/PemRoundTrip.java:10: error: PEMEncoder is a preview API and is disabled by default.
+		String pem = PEMEncoder.of().encodeToString(kp.getPublic());
+		             ^
+--- JDK 25, --enable-preview:
+-----BEGIN PUBLIC KEY-----
+round trip equal: true
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+# 05-json-incubator (JEP 540): JsonDemo.java on JDK 28
+--- module and API surface:
+jdk.incubator.json@28-ea
+exports jdk.incubator.json
+requires java.base mandated
+  public static jdk.incubator.json.JsonValue parse(java.lang.String);
+  public static jdk.incubator.json.JsonValue parse(char[]);
+  public static java.lang.String toDisplayString(jdk.incubator.json.JsonValue, java.lang.String);
+--- without --add-modules:
+src/JsonDemo.java:1: error: package jdk.incubator.json is not visible
+import jdk.incubator.json.*;
+--- with --add-modules jdk.incubator.json:
+name = Ada
+second language = fr
+age + 1 = 37
+missing key -> Optional.empty
+{
+  "name": "Ada",
+  "langs": [
+    "en",
+    "fr"
+  ],
+  "age": 36
+}
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+# 06-shenandoah (JEP 535: generational mode by default)
+--- JDK 28 EA build, -XX:+UseShenandoahGC:
+Error occurred during initialization of VM
+Option -XX:+UseShenandoahGC not supported
+--- JDK 25 Temurin, -XX:+UseShenandoahGC -Xlog:gc*:
+[0.007s][info][gc     ] Using Shenandoah
+[0.009s][info][gc,init] Mode: Snapshot-At-The-Beginning (SATB)
+[0.016s][info][gc,metaspace] CDS archive(s) mapped at: [0x0000000020000000-0x0000000020d96000-0x0000000020d96000), size 14245888, SharedBaseAddress: 0x0000000020000000, ArchiveRelocationMode: 1.
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+# 07-jep-status (quoted from published articles on 2026-09-28; NOT produced by running code; status changes weekly)
+InfoQ, "JDK 27 and JDK 28: What We Know So Far" (https://www.infoq.com/news/2026/08/java-27-so-far/), August 2026:
+  Targeted to JDK 28: JEP 541 Deprecate the macOS/x64 Port for Removal; JEP 540 Simple JSON API (Incubator);
+  JEP 539 Strict Field Initialization in the JVM (Preview); JEP 535 Shenandoah GC: Generational Mode by Default; JEP 401 Value Objects (Preview)
+  Proposed to target: JEP 542 PEM Encodings of Cryptographic Objects
+  "Scheduled for a GA release in March 2027"
+Inside.java, 2026-09-20 (https://inside.java/2026/09/20/jep401-target-jdk28/): "JEP targeted to JDK 28: 401: Value Objects (Preview)"