JDK14 RFR of JDK-8234381: API docs should mention special handling of enums in serialization

[Joe Darcy]

Hello,

Please review this small doc changes to more explicitly discuss the 
special handling of enum types by serialization:

     JDK-8234381: API docs should mention special handling of enums in 
serialization
     http://cr.openjdk.java.net/~darcy/8234381.0/

Patch below; thanks,

-Joe

--- old/src/java.base/share/classes/java/io/Serializable.java 2019-11-19 
10:17:45.803443000 -0800
+++ new/src/java.base/share/classes/java/io/Serializable.java 2019-11-19 
10:17:45.399241001 -0800
@@ -134,6 +134,11 @@
   * This readResolve method follows the same invocation rules and
   * accessibility rules as writeReplace.<p>
   *
+ * <p>Enum types are all serializable and receive treatment defined by
+ * the <cite>Java Object Serialization Specification</cite> during
+ * serialization and deserialization. Any declarations of the special
+ * handling methods discussed above are ignored for enum types.
+ *
   * The serialization runtime associates with each serializable class a 
version
   * number, called a serialVersionUID, which is used during 
deserialization to
   * verify that the sender and receiver of a serialized object have loaded
@@ -152,8 +157,9 @@
   * If a serializable class does not explicitly declare a 
serialVersionUID, then
   * the serialization runtime will calculate a default serialVersionUID 
value
   * for that class based on various aspects of the class, as described 
in the
- * Java(TM) Object Serialization Specification.  However, it is 
<em>strongly
- * recommended</em> that all serializable classes explicitly declare
+ * Java Object Serialization Specification.  This specification defines the
+ * serialVersionUID of an enum type to be 0L. However, it is <em>strongly
+ * recommended</em> that all serializable classes other than enum types 
explicitly declare
   * serialVersionUID values, since the default serialVersionUID 
computation is
   * highly sensitive to class details that may vary depending on compiler
   * implementations, and can thus result in unexpected
--- old/src/java.base/share/classes/java/lang/Enum.java 2019-11-19 
10:17:46.807945000 -0800
+++ new/src/java.base/share/classes/java/lang/Enum.java 2019-11-19 
10:17:46.371727000 -0800
@@ -47,6 +47,13 @@
   * found in section 8.9 of
   * <cite>The Java™ Language Specification</cite>.
   *
+ * Enumeration types are all serializable and receive special handling
+ * by the serialization mechanism. The serialized representation used
+ * for enum constants cannot be customized. Declarations of methods
+ * and fields that would otherwise interact with serialization are
+ * ignored, including {@code serialVersionUID}; see the <cite>Java
+ * Object Serialization Specification</cite> for details.
+ *
   * <p> Note that when using an enumeration type as the type of a set
   * or as the type of the keys in a map, specialized and efficient
   * {@linkplain java.util.EnumSet set} and {@linkplain