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

*** 39,48 ****
--- 39,49 ----
   * @author  Frank Yellin
   * @jls 11.2 Compile-Time Checking of Exceptions
   * @since   1.0
   */
  public class RuntimeException extends Exception {
+     @java.io.Serial
      static final long serialVersionUID = -7034897190745766939L;
  
      /** Constructs a new runtime exception with {@code null} as its
       * detail message.  The cause is not initialized, and may subsequently be
       * initialized by a call to {@link #initCause}.