src/java.base/share/classes/java/lang/StringBuffer.java

*** 113,122 ****
--- 113,123 ----
       * whenever the StringBuffer is modified.
       */
      private transient String toStringCache;
  
      /** use serialVersionUID from JDK 1.0.2 for interoperability */
+     @java.io.Serial
      static final long serialVersionUID = 3388685877147921107L;
  
      /**
       * Constructs a string buffer with no characters in it and an
       * initial capacity of 16 characters.
*** 721,730 ****
--- 722,732 ----
       *              The number of characters in this StringBuffer.
       * @serialField shared  boolean
       *              A flag indicating whether the backing array is shared.
       *              The value is ignored upon deserialization.
       */
+     @java.io.Serial
      private static final java.io.ObjectStreamField[] serialPersistentFields =
      {
          new java.io.ObjectStreamField("value", char[].class),
          new java.io.ObjectStreamField("count", Integer.TYPE),
          new java.io.ObjectStreamField("shared", Boolean.TYPE),
*** 732,741 ****
--- 734,744 ----
  
      /**
       * readObject is called to restore the state of the StringBuffer from
       * a stream.
       */
+     @java.io.Serial
      private synchronized void writeObject(java.io.ObjectOutputStream s)
          throws java.io.IOException {
          java.io.ObjectOutputStream.PutField fields = s.putFields();
          char[] val = new char[capacity()];
          if (isLatin1()) {
*** 751,760 ****
--- 754,764 ----
  
      /**
       * readObject is called to restore the state of the StringBuffer from
       * a stream.
       */
+     @java.io.Serial
      private void readObject(java.io.ObjectInputStream s)
          throws java.io.IOException, ClassNotFoundException {
          java.io.ObjectInputStream.GetField fields = s.readFields();
          char[] val = (char[])fields.get("value", null);
          initBytes(val, 0, val.length);