/*

 * Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.lang;

/**

 * Thrown when an application attempts to use {@code null} in a

 * case where an object is required. These include:

 * <ul>

 * <li>Calling the instance method of a {@code null} object.

 * <li>Accessing or modifying the field of a {@code null} object.

 * <li>Taking the length of {@code null} as if it were an array.

 * <li>Accessing or modifying the slots of {@code null} as if it

 *     were an array.

 * <li>Throwing {@code null} as if it were a {@code Throwable}

 *     value.

 * </ul>

 * <p>

 * Applications should throw instances of this class to indicate

 * other illegal uses of the {@code null} object.

 *

 * {@code NullPointerException} objects may be constructed by the

 * virtual machine as if {@linkplain Throwable#Throwable(String,

 * Throwable, boolean, boolean) suppression were disabled and/or the

 * stack trace was not writable}.

 *

 * @author  unascribed

 * @since   1.0

 */

public class NullPointerException extends RuntimeException {

    @java.io.Serial

    private static final long serialVersionUID = 5162710183389028792L;

    /**

     * Constructs a {@code NullPointerException} with no detail message.

     */

    public NullPointerException() {

        super();

    }

    /**

     * Constructs a {@code NullPointerException} with the specified

     * detail message.

     *

     * @param   s   the detail message.

     */

    public NullPointerException(String s) {

        super(s);

    }

    /**

     * Returns the detail message string of this throwable.

     *

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

     * returned. Otherwise, an implementation specific message or

     * {@code null} is returned.

     *

     * @implNote

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

     * long as certain internal information is available, a verbose

     * description of the null reference is returned.

     * The internal information is not available in deserialized

     * NullPointerExceptions.

     *

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

     */

    public String getMessage() {

        String message = super.getMessage();

        if (message == null) {

            return getExtendedNPEMessage();

        }

        return message;

    }

    /**

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

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

     * exceptions where this is not applicable.

     */

    private native String getExtendedNPEMessage();

}