--- old/src/java.base/share/classes/java/net/URL.java	2019-08-27 17:28:05.854324386 -0700
+++ new/src/java.base/share/classes/java/net/URL.java	2019-08-27 17:28:05.682324386 -0700
@@ -175,6 +175,7 @@
 public final class URL implements java.io.Serializable {
 
     static final String BUILTIN_HANDLERS_PREFIX = "sun.net.www.protocol";
+    @java.io.Serial
     static final long serialVersionUID = -7627629688361524110L;
 
     /**
@@ -1489,6 +1490,7 @@
      * @serialField    hashCode int
      *
      */
+    @java.io.Serial
     private static final ObjectStreamField[] serialPersistentFields = {
         new ObjectStreamField("protocol", String.class),
         new ObjectStreamField("host", String.class),
@@ -1508,6 +1510,7 @@
      * the protocol variable returns a valid URLStreamHandler and
      * throw an IOException if it does not.
      */
+    @java.io.Serial
     private synchronized void writeObject(java.io.ObjectOutputStream s)
         throws IOException
     {
@@ -1519,6 +1522,7 @@
      * stream.  It reads the components of the URL and finds the local
      * stream handler.
      */
+    @java.io.Serial
     private synchronized void readObject(java.io.ObjectInputStream s)
             throws IOException, ClassNotFoundException {
         GetField gf = s.readFields();
@@ -1550,7 +1554,7 @@
      * @throws ObjectStreamException if a new object replacing this
      * object could not be created
      */
-
+   @java.io.Serial
    private Object readResolve() throws ObjectStreamException {
 
         URLStreamHandler handler = null;