1 /* 2 * Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang; 27 28 /** 29 * Thrown when an application attempts to use {@code null} in a 30 * case where an object is required. These include: 31 * <ul> 32 * <li>Calling the instance method of a {@code null} object. 33 * <li>Accessing or modifying the field of a {@code null} object. 34 * <li>Taking the length of {@code null} as if it were an array. 35 * <li>Accessing or modifying the slots of {@code null} as if it 36 * were an array. 37 * <li>Throwing {@code null} as if it were a {@code Throwable} 38 * value. 39 * </ul> 40 * <p> 41 * Applications should throw instances of this class to indicate 42 * other illegal uses of the {@code null} object. 43 * 44 * {@code NullPointerException} objects may be constructed by the 45 * virtual machine as if {@linkplain Throwable#Throwable(String, 46 * Throwable, boolean, boolean) suppression were disabled and/or the 47 * stack trace was not writable}. 48 * 49 * @author unascribed 50 * @since 1.0 51 */ 52 public class NullPointerException extends RuntimeException { 53 @java.io.Serial 54 private static final long serialVersionUID = 5162710183389028792L; 55 56 /** 57 * Constructs a {@code NullPointerException} with no detail message. 58 */ NullPointerException()59 public NullPointerException() { 60 super(); 61 } 62 63 /** 64 * Constructs a {@code NullPointerException} with the specified 65 * detail message. 66 * 67 * @param s the detail message. 68 */ NullPointerException(String s)69 public NullPointerException(String s) { 70 super(s); 71 } 72 73 /** 74 * Returns the detail message string of this throwable. 75 * 76 * <p> If a non-null message was supplied in a constructor it is 77 * returned. Otherwise, an implementation specific message or 78 * {@code null} is returned. 79 * 80 * @implNote 81 * If no explicit message was passed to the constructor, and as 82 * long as certain internal information is available, a verbose 83 * description of the null reference is returned. 84 * The internal information is not available in deserialized 85 * NullPointerExceptions. 86 * 87 * @return the detail message string, which may be {@code null}. 88 */ getMessage()89 public String getMessage() { 90 String message = super.getMessage(); 91 if (message == null) { 92 return getExtendedNPEMessage(); 93 } 94 return message; 95 } 96 97 /** 98 * Get an extended exception message. This returns a string describing 99 * the location and cause of the exception. It returns null for 100 * exceptions where this is not applicable. 101 */ getExtendedNPEMessage()102 private native String getExtendedNPEMessage(); 103 } 104