1 /* 2 * Copyright (c) 1994, 2020, 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 * @since 1.0 50 */ 51 public class NullPointerException extends RuntimeException { 52 @java.io.Serial 53 private static final long serialVersionUID = 5162710183389028792L; 54 55 /** 56 * Constructs a {@code NullPointerException} with no detail message. 57 */ NullPointerException()58 public NullPointerException() { 59 super(); 60 } 61 62 /** 63 * Constructs a {@code NullPointerException} with the specified 64 * detail message. 65 * 66 * @param s the detail message. 67 */ NullPointerException(String s)68 public NullPointerException(String s) { 69 super(s); 70 } 71 72 // BEGIN Android-removed: no extended NPEs in Android. 73 /* 74 // 0: no backtrace filled in, no message computed. 75 // 1: backtrace filled in, no message computed. 76 // 2: message computed 77 private transient int extendedMessageState; 78 private transient String extendedMessage; 79 80 /** 81 * {@inheritDoc} 82 * 83 public synchronized Throwable fillInStackTrace() { 84 // If the stack trace is changed the extended NPE algorithm 85 // will compute a wrong message. So compute it beforehand. 86 if (extendedMessageState == 0) { 87 extendedMessageState = 1; 88 } else if (extendedMessageState == 1) { 89 extendedMessage = getExtendedNPEMessage(); 90 extendedMessageState = 2; 91 } 92 return super.fillInStackTrace(); 93 } 94 95 /** 96 * Returns the detail message string of this throwable. 97 * 98 * <p> If a non-null message was supplied in a constructor it is 99 * returned. Otherwise, an implementation specific message or 100 * {@code null} is returned. 101 * 102 * @implNote 103 * If no explicit message was passed to the constructor, and as 104 * long as certain internal information is available, a verbose 105 * description of the null reference is returned. 106 * The internal information is not available in deserialized 107 * NullPointerExceptions. 108 * 109 * @return the detail message string, which may be {@code null}. 110 * 111 public String getMessage() { 112 String message = super.getMessage(); 113 if (message == null) { 114 synchronized(this) { 115 if (extendedMessageState == 1) { 116 // Only the original stack trace was filled in. Message will 117 // compute correctly. 118 extendedMessage = getExtendedNPEMessage(); 119 extendedMessageState = 2; 120 } 121 return extendedMessage; 122 } 123 } 124 return message; 125 } 126 127 /** 128 * Get an extended exception message. This returns a string describing 129 * the location and cause of the exception. It returns null for 130 * exceptions where this is not applicable. 131 * 132 private native String getExtendedNPEMessage(); 133 */ 134 // END Android-removed: no extended NPEs in Android. 135 } 136