diff a/src/java.base/share/classes/javax/security/auth/Subject.java b/src/java.base/share/classes/javax/security/auth/Subject.java
--- a/src/java.base/share/classes/javax/security/auth/Subject.java
+++ b/src/java.base/share/classes/javax/security/auth/Subject.java
@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 1998, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2021, 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
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this
@@ -947,10 +947,13 @@
         }
     }
 
     /**
      * Writes this object out to a stream (i.e., serializes it).
+     *
+     * @param  oos the {@code ObjectOutputStream} to which data is written
+     * @throws IOException if an I/O error occurs
      */
     @java.io.Serial
     private void writeObject(java.io.ObjectOutputStream oos)
                 throws java.io.IOException {
         synchronized(principals) {
@@ -958,10 +961,14 @@
         }
     }
 
     /**
      * Reads this object from a stream (i.e., deserializes it)
+     *
+     * @param  s the {@code ObjectInputStream} from which data is read
+     * @throws IOException if an I/O error occurs
+     * @throws ClassNotFoundException if a serialized class cannot be loaded
      */
     @SuppressWarnings("unchecked")
     @java.io.Serial
     private void readObject(java.io.ObjectInputStream s)
                 throws java.io.IOException, ClassNotFoundException {
@@ -1406,10 +1413,13 @@
          * @serialData If this is a private credential set,
          *      a security check is performed to ensure that
          *      the caller has permission to access each credential
          *      in the set.  If the security check passes,
          *      the set is serialized.
+         *
+         * @param  oos the {@code ObjectOutputStream} to which data is written
+         * @throws IOException if an I/O error occurs
          */
         @java.io.Serial
         private void writeObject(java.io.ObjectOutputStream oos)
                 throws java.io.IOException {
 
@@ -1425,10 +1435,17 @@
             fields.put("elements", elements);
             fields.put("which", which);
             oos.writeFields();
         }
 
+        /**
+         * Restores the state of this object from the stream.
+         *
+         * @param  ois the {@code ObjectInputStream} from which data is read
+         * @throws IOException if an I/O error occurs
+         * @throws ClassNotFoundException if a serialized class cannot be loaded
+         */
         @SuppressWarnings("unchecked")
         @java.io.Serial
         private void readObject(ObjectInputStream ois)
             throws IOException, ClassNotFoundException
         {
