diff -r 18863bf3501f -r e0b8b019d2f5 src/java.base/share/classes/java/util/HashMap.java
--- a/src/java.base/share/classes/java/util/HashMap.java	Thu Aug 29 18:52:30 2019 -0400
+++ b/src/java.base/share/classes/java/util/HashMap.java	Thu Aug 29 16:31:34 2019 -0700
@@ -138,6 +138,7 @@
 public class HashMap<K,V> extends AbstractMap<K,V>
     implements Map<K,V>, Cloneable, Serializable {
 
+    @java.io.Serial
     private static final long serialVersionUID = 362498820763181265L;
 
     /*
@@ -1489,6 +1490,7 @@
      *             for each key-value mapping.  The key-value mappings are
      *             emitted in no particular order.
      */
+    @java.io.Serial
     private void writeObject(java.io.ObjectOutputStream s)
         throws IOException {
         int buckets = capacity();
@@ -1506,6 +1508,7 @@
      *         could not be found
      * @throws IOException if an I/O error occurs
      */
+    @java.io.Serial
     private void readObject(java.io.ObjectInputStream s)
         throws IOException, ClassNotFoundException {
         // Read in the threshold (ignored), loadfactor, and any hidden stuff