8251160: Fix "no comment" warnings in java.logging

Add missing documentation to the Serialized Form of Level and LogRecord.

Reviewed-by: lancea, mchung

Author: dfuch

src/java.logging/share/classes/java/util/logging/Level.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2020, 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
@@ -25,6 +25,7 @@
 
 package java.util.logging;
 
+import java.io.Serial;
 import java.lang.ref.Reference;
 import java.lang.ref.ReferenceQueue;
 import java.lang.ref.WeakReference;
@@ -432,11 +433,20 @@ public final int intValue() {
         return value;
     }
 
+    @Serial
     private static final long serialVersionUID = -8176160795706313070L;
 
-    // Serialization magic to prevent "doppelgangers".
-    // This is a performance optimization.
+    /**
+     * Returns a {@code Level} instance with the same {@code name},
+     * {@code value}, and {@code resourceBundleName} as the deserialized
+     * object.
+     * @return a {@code Level} instance corresponding to the deserialized
+     * object.
+     */
+    @Serial
     private Object readResolve() {
+        // Serialization magic to prevent "doppelgangers".
+        // This is a performance optimization.
         Optional<Level> level = KnownLevel.matches(this);
         if (level.isPresent()) {
             return level.get();

src/java.logging/share/classes/java/util/logging/LogRecord.java

@@ -599,6 +599,10 @@ public void setThrown(Throwable thrown) {
      * by String values for each parameter.  If a parameter is null, then
      * a null String is written.  Otherwise the output of Object.toString()
      * is written.
+     *
+     * @param out the {@code ObjectOutputStream} to write to
+     *
+     * @throws  IOException if I/O errors occur
      */
     @Serial
     private void writeObject(ObjectOutputStream out) throws IOException {
@@ -647,6 +651,14 @@ private void writeObject(ObjectOutputStream out) throws IOException {
      * {@code threadID} which may be anything between {@code Integer.MIN_VALUE}
      * and {Integer.MAX_VALUE}.
      * </ul>
+     *
+     * See {@code writeObject} for a description of the serial form.
+     *
+     * @param in the {@code ObjectInputStream} to read from
+     *
+     * @throws  ClassNotFoundException if the class of a serialized object
+     *          could not be found.
+     * @throws  IOException if an I/O error occurs.
      */
     @Serial
     private void readObject(ObjectInputStream in)