src/java.base/share/classes/java/util/BitSet.java

@@ -81,10 +81,11 @@
      *
      * The bits in this BitSet.  The ith bit is stored in bits[i/64] at
      * bit position i % 64 (where bit position 0 refers to the least
      * significant bit and 63 refers to the most significant bit).
      */
+    @java.io.Serial
     private static final ObjectStreamField[] serialPersistentFields = {
         new ObjectStreamField("bits", long[].class),
     };
 
     /**

@@ -102,10 +103,11 @@
      * the user knows what he's doing and try harder to preserve it.
      */
     private transient boolean sizeIsSticky = false;
 
     /* use serialVersionUID from JDK 1.0.2 for interoperability */
+    @java.io.Serial
     private static final long serialVersionUID = 7997698588986878753L;
 
     /**
      * Given a bit index, return word index containing it.
      */

@@ -1122,10 +1124,11 @@
 
     /**
      * Save the state of the {@code BitSet} instance to a stream (i.e.,
      * serialize it).
      */
+    @java.io.Serial
     private void writeObject(ObjectOutputStream s)
         throws IOException {
 
         checkInvariants();
 

@@ -1139,10 +1142,11 @@
 
     /**
      * Reconstitute the {@code BitSet} instance from a stream (i.e.,
      * deserialize it).
      */
+    @java.io.Serial
     private void readObject(ObjectInputStream s)
         throws IOException, ClassNotFoundException {
 
         ObjectInputStream.GetField fields = s.readFields();
         words = (long[]) fields.get("bits", null);