feat(jdk14): add JEP 363 - Remove the Concurrent Mark Sweep (CMS) Garbage Collector (#348)

* feat(java14): add JEP 363 - Remove the Concurrent Mark Sweep (CMS) Garbage Collector
* fix: JSON metadata for JEP 363

Author: YuuuuuuYu

src/main/java/org/javademos/init/Java14DemoLoader.java

@@ -12,6 +12,7 @@
 import org.javademos.java14.jep359.RecordsPreviewDemo;
 import org.javademos.java14.jep361.SwitchExpressionsDemo;
 import org.javademos.java14.jep362.SolarisSparcRemovalDemo;
+import org.javademos.java14.jep363.RemoveTheCMSGarbageCollectorDemo;
 import org.javademos.java14.jep364.ZGarbageCollectorOnMacOS;
 import org.javademos.java14.jep365.ZGarbageCollectorOnWindows;
 import org.javademos.java14.jep366.ParallelScavengeGCCombinationDemo;
@@ -32,6 +33,7 @@ public void loadDemos(Map<Integer, IDemo> demos) {
         demos.put(359, new RecordsPreviewDemo());
         demos.put(361, new SwitchExpressionsDemo());
         demos.put(362, new SolarisSparcRemovalDemo());
+        demos.put(363, new RemoveTheCMSGarbageCollectorDemo());
         demos.put(364, new ZGarbageCollectorOnMacOS());
         demos.put(365, new ZGarbageCollectorOnWindows());
         demos.put(366, new ParallelScavengeGCCombinationDemo());

src/main/java/org/javademos/java14/jep363/RemoveTheCMSGarbageCollectorDemo.java

@@ -0,0 +1,59 @@
+package org.javademos.java14.jep363;
+
+import org.javademos.commons.IDemo;
+
+/// Demo for JDK 14 feature JEP 363 - Remove the Concurrent Mark Sweep (CMS) Garbage Collector.
+///
+/// JEP history:
+/// - JDK 14: [JEP 363 - Remove the Concurrent Mark Sweep (CMS) Garbage Collector](https://openjdk.org/jeps/363)
+/// - JDK 9: [JEP 291 - Deprecate the Concurrent Mark Sweep (CMS) Garbage Collector](https://openjdk.org/jeps/291)
+///
+/// @author yuuuuuuyu
+
+public class RemoveTheCMSGarbageCollectorDemo implements IDemo {
+    @Override
+    public void demo() {
+        info(363);
+
+        // The Concurrent Mark Sweep (CMS) garbage collector was a low-pause GC
+        // designed for applications requiring shorter stop-the-world times.
+        // It performed part of its mark-and-sweep phases concurrently with
+        // running application threads.
+        //
+        // However, CMS had several drawbacks:
+        // - High maintenance cost and complex code base in HotSpot.
+        // - Fragmentation issues due to the non-compacting nature of CMS.
+        // - Poor scalability and unpredictable long pauses on large heaps.
+        //
+        // Because modern GCs like G1 (JEP 248), ZGC (JEP 333), and Shenandoah
+        // offer better latency and throughput characteristics,
+        // CMS was first deprecated in JDK 9 (JEP 291) and completely removed
+        // in JDK 14 under JEP 363.
+        //
+        // As of JDK 14 and later, the JVM ignores the option
+        // "-XX:+UseConcMarkSweepGC" and prints a warning message instead:
+        // "Ignoring option UseConcMarkSweepGC; support was removed in 14.0"
+        //
+        // e.g. (jdk 11) `java -XX:+UseConcMarkSweepGC -version`
+        // result:
+        //      OpenJDK 64-Bit Server VM warning: Option UseConcMarkSweepGC was deprecated in version 9.0 and will likely be removed in a future release.
+        //      openjdk version "11.0.28" 2025-07-15 LTS
+        //      OpenJDK Runtime Environment Microsoft-11913448 (build 11.0.28+6-LTS)
+        //      OpenJDK 64-Bit Server VM Microsoft-11913448 (build 11.0.28+6-LTS, mixed mode, sharing)
+        //
+        // e.g. (jdk 17, 25) `java -XX:+UseConcMarkSweepGC -version`
+        // result:
+        //      Unrecognized VM option 'UseConcMarkSweepGC'
+        //      Error: Could not create the Java Virtual Machine.
+        //      Error: A fatal exception has occurred. Program will exit
+        //
+        // Developers migrating from older Java versions should replace CMS
+        // with modern collectors such as:
+        //   - G1GC (default since JDK 9)
+        //   - ZGC for ultra-low latency workloads
+        //   - Shenandoah for concurrent compaction
+        //
+        // No source-level code changes are required — only JVM options and
+        // performance tuning scripts need to be updated when upgrading.
+    }
+}

src/main/resources/JDK14Info.json

@@ -55,6 +55,14 @@
     "link": true,
     "code": false
   },
+  {
+    "jep": 363,
+    "jdk": 14,
+    "name": "JEP 363 - Remove the Concurrent Mark Sweep (CMS) Garbage Collector",
+    "dscr": "Remove the Concurrent Mark Sweep (CMS) garbage collector.",
+    "link": false,
+    "code": false
+  },
   {
     "jep": 364,
     "jdk": 14,