73 

    74     /**

    75      * Returns the detail message string of this throwable.

    76      *

    77      * <p> If a non-null message was supplied in a constructor it is

    78      * returned. Otherwise, an implementation specific message or

    79      * {@code null} is returned.

    80      *

    81      * @implNote

    82      * If no explicit message was passed to the constructor, and as

    83      * long as certain internal information is available, a verbose

    84      * description of the null reference is returned.

    85      * The internal information is not available in deserialized

    86      * NullPointerExceptions.

    87      *

    88      * @return the detail message string, which may be {@code null}.

    89      */

    90     public String getMessage() {

    91         String message = super.getMessage();

    92         if (message == null) {

    93             return getExtendedNPEMessage();

    94         }

    95         return message;

    96     }

    97 

    98     /**

    99      * Get an extended exception message. This returns a string describing

   100      * the location and cause of the exception. It returns null for

   101      * exceptions where this is not applicable.

   102      */

   103     private native String getExtendedNPEMessage();