Automatic merge of jdk:master into master

Author: duke

src/java.base/share/classes/java/time/ZoneId.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -169,14 +169,14 @@
  * The {@code equals} method should be used for comparisons.
  *
  * @implSpec
- * This abstract class has two implementations, both of which are immutable and thread-safe.
- * One implementation models region-based IDs, the other is {@code ZoneOffset} modelling
- * offset-based IDs. This difference is visible in serialization.
+ * This abstract sealed class permits two implementations, both of which are immutable and
+ * thread-safe. One implementation models region-based IDs, the other is {@code ZoneOffset}
+ * modelling offset-based IDs. This difference is visible in serialization.
  *
  * @since 1.8
  */
 @jdk.internal.ValueBased
-public abstract class ZoneId implements Serializable {
+public abstract sealed class ZoneId implements Serializable permits ZoneOffset, ZoneRegion {
 
     /**
      * A map of zone overrides to enable the short time-zone names to be used.
@@ -471,11 +471,7 @@ public static ZoneId from(TemporalAccessor temporal) {
     /**
      * Constructor only accessible within the package.
      */
-    ZoneId() {
-        if (getClass() != ZoneOffset.class && getClass() != ZoneRegion.class) {
-            throw new AssertionError("Invalid subclass");
-        }
-    }
+    ZoneId() {}
 
     //-----------------------------------------------------------------------
     /**