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

@@ -170,10 +170,11 @@
      * us to avoid recalculating this.
      */
     private boolean hashIsZero; // Default to false;
 
     /** use serialVersionUID from JDK 1.0.2 for interoperability */
+    @java.io.Serial
     private static final long serialVersionUID = -6849794470754667710L;
 
     /**
      * If String compaction is disabled, the bytes in {@code value} are
      * always encoded in UTF16.

@@ -222,10 +223,11 @@
      *
      * A String instance is written into an ObjectOutputStream according to
      * <a href="{@docRoot}/../specs/serialization/protocol.html#stream-elements">
      * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
      */
+    @java.io.Serial
     private static final ObjectStreamField[] serialPersistentFields =
         new ObjectStreamField[0];
 
     /**
      * Initializes a newly created {@code String} object so that it represents

@@ -1233,10 +1235,11 @@
     public static final Comparator<String> CASE_INSENSITIVE_ORDER
                                          = new CaseInsensitiveComparator();
     private static class CaseInsensitiveComparator
             implements Comparator<String>, java.io.Serializable {
         // use serialVersionUID from JDK 1.2.2 for interoperability
+        @java.io.Serial
         private static final long serialVersionUID = 8575799808933029326L;
 
         public int compare(String s1, String s2) {
             byte v1[] = s1.value;
             byte v2[] = s2.value;

@@ -1248,10 +1251,11 @@
             return coder == LATIN1 ? StringLatin1.compareToCI_UTF16(v1, v2)
                                    : StringUTF16.compareToCI_Latin1(v1, v2);
         }
 
         /** Replaces the de-serialized object. */
+        @java.io.Serial
         private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
     }
 
     /**
      * Compares two strings lexicographically, ignoring case