src/java.base/share/classes/java/lang/NullPointerException.java
author goetz
Mon, 14 Oct 2019 11:36:17 +0200
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parent 57956 e0b8b019d2f5
child 58679 9c3209ff7550
child 59201 b24f4caa1411
permissions -rw-r--r--
8218628: Add detailed message to NullPointerException describing what is null. Summary: This is the implementation of JEP 358: Helpful NullPointerExceptions. Reviewed-by: coleenp, clanger, rschmelter, rriggs, forax, mr
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/*
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 * Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.  Oracle designates this
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 * particular file as subject to the "Classpath" exception as provided
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 * by Oracle in the LICENSE file that accompanied this code.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 */
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package java.lang;
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/**
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 * Thrown when an application attempts to use {@code null} in a
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 * case where an object is required. These include:
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 * <ul>
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 * <li>Calling the instance method of a {@code null} object.
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 * <li>Accessing or modifying the field of a {@code null} object.
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 * <li>Taking the length of {@code null} as if it were an array.
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 * <li>Accessing or modifying the slots of {@code null} as if it
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 *     were an array.
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 * <li>Throwing {@code null} as if it were a {@code Throwable}
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 *     value.
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 * </ul>
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 * <p>
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 * Applications should throw instances of this class to indicate
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 * other illegal uses of the {@code null} object.
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 *
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 * {@code NullPointerException} objects may be constructed by the
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 * virtual machine as if {@linkplain Throwable#Throwable(String,
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 * Throwable, boolean, boolean) suppression were disabled and/or the
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 * stack trace was not writable}.
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 *
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 * @author  unascribed
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 * @since   1.0
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 */
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public
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class NullPointerException extends RuntimeException {
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    @java.io.Serial
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    private static final long serialVersionUID = 5162710183389028792L;
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    /**
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     * Constructs a {@code NullPointerException} with no detail message.
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     */
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    public NullPointerException() {
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        super();
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    }
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    /**
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     * Constructs a {@code NullPointerException} with the specified
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     * detail message.
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     *
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     * @param   s   the detail message.
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     */
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    public NullPointerException(String s) {
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        super(s);
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    }
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    /**
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     * Returns the detail message string of this throwable.
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     *
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     * <p> If a non-null message was supplied in a constructor it is
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     * returned. Otherwise, an implementation specific message or
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     * {@code null} is returned.
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     *
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     * @implNote
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     * If no explicit message was passed to the constructor, and as
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     * long as certain internal information is available, a verbose
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     * description of the null reference is returned.
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     * The internal information is not available in deserialized
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     * NullPointerExceptions.
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     *
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     * @return the detail message string, which may be {@code null}.
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     */
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    public String getMessage() {
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        String message = super.getMessage();
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        if (message == null) {
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            return getExtendedNPEMessage();
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        }
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        return message;
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    }
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    /**
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     * Get an extended exception message. This returns a string describing
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     * the location and cause of the exception. It returns null for
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     * exceptions where this is not applicable.
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     */
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    private native String getExtendedNPEMessage();
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}