1 /* 2 * Copyright (c) 2000, 2013, 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 import java.util.Objects; 29 30 /** 31 * An element in a stack trace, as returned by {@link 32 * Throwable#getStackTrace()}. Each element represents a single stack frame. 33 * All stack frames except for the one at the top of the stack represent 34 * a method invocation. The frame at the top of the stack represents the 35 * execution point at which the stack trace was generated. Typically, 36 * this is the point at which the throwable corresponding to the stack trace 37 * was created. 38 * 39 * @since 1.4 40 * @author Josh Bloch 41 */ 42 public final class StackTraceElement implements java.io.Serializable { 43 // Normally initialized by VM (public constructor added in 1.5) 44 private String declaringClass; 45 private String methodName; 46 private String fileName; 47 private int lineNumber; 48 49 /** 50 * Creates a stack trace element representing the specified execution 51 * point. 52 * 53 * @param declaringClass the fully qualified name of the class containing 54 * the execution point represented by the stack trace element 55 * @param methodName the name of the method containing the execution point 56 * represented by the stack trace element 57 * @param fileName the name of the file containing the execution point 58 * represented by the stack trace element, or {@code null} if 59 * this information is unavailable 60 * @param lineNumber the line number of the source line containing the 61 * execution point represented by this stack trace element, or 62 * a negative number if this information is unavailable. A value 63 * of -2 indicates that the method containing the execution point 64 * is a native method 65 * @throws NullPointerException if {@code declaringClass} or 66 * {@code methodName} is null 67 * @since 1.5 68 */ StackTraceElement(String declaringClass, String methodName, String fileName, int lineNumber)69 public StackTraceElement(String declaringClass, String methodName, 70 String fileName, int lineNumber) { 71 this.declaringClass = Objects.requireNonNull(declaringClass, "Declaring class is null"); 72 this.methodName = Objects.requireNonNull(methodName, "Method name is null"); 73 this.fileName = fileName; 74 this.lineNumber = lineNumber; 75 } 76 77 /** 78 * Returns the name of the source file containing the execution point 79 * represented by this stack trace element. Generally, this corresponds 80 * to the {@code SourceFile} attribute of the relevant {@code class} 81 * file (as per <i>The Java Virtual Machine Specification</i>, Section 82 * 4.7.7). In some systems, the name may refer to some source code unit 83 * other than a file, such as an entry in source repository. 84 * 85 * @return the name of the file containing the execution point 86 * represented by this stack trace element, or {@code null} if 87 * this information is unavailable. 88 */ getFileName()89 public String getFileName() { 90 return fileName; 91 } 92 93 /** 94 * Returns the line number of the source line containing the execution 95 * point represented by this stack trace element. Generally, this is 96 * derived from the {@code LineNumberTable} attribute of the relevant 97 * {@code class} file (as per <i>The Java Virtual Machine 98 * Specification</i>, Section 4.7.8). 99 * 100 * @return the line number of the source line containing the execution 101 * point represented by this stack trace element, or a negative 102 * number if this information is unavailable. 103 */ getLineNumber()104 public int getLineNumber() { 105 return lineNumber; 106 } 107 108 /** 109 * Returns the fully qualified name of the class containing the 110 * execution point represented by this stack trace element. 111 * 112 * @return the fully qualified name of the {@code Class} containing 113 * the execution point represented by this stack trace element. 114 */ getClassName()115 public String getClassName() { 116 return declaringClass; 117 } 118 119 /** 120 * Returns the name of the method containing the execution point 121 * represented by this stack trace element. If the execution point is 122 * contained in an instance or class initializer, this method will return 123 * the appropriate <i>special method name</i>, {@code <init>} or 124 * {@code <clinit>}, as per Section 3.9 of <i>The Java Virtual 125 * Machine Specification</i>. 126 * 127 * @return the name of the method containing the execution point 128 * represented by this stack trace element. 129 */ getMethodName()130 public String getMethodName() { 131 return methodName; 132 } 133 134 /** 135 * Returns true if the method containing the execution point 136 * represented by this stack trace element is a native method. 137 * 138 * @return {@code true} if the method containing the execution point 139 * represented by this stack trace element is a native method. 140 */ isNativeMethod()141 public boolean isNativeMethod() { 142 return lineNumber == -2; 143 } 144 145 /** 146 * Returns a string representation of this stack trace element. The 147 * format of this string depends on the implementation, but the following 148 * examples may be regarded as typical: 149 * <ul> 150 * <li> 151 * {@code "MyClass.mash(MyClass.java:9)"} - Here, {@code "MyClass"} 152 * is the <i>fully-qualified name</i> of the class containing the 153 * execution point represented by this stack trace element, 154 * {@code "mash"} is the name of the method containing the execution 155 * point, {@code "MyClass.java"} is the source file containing the 156 * execution point, and {@code "9"} is the line number of the source 157 * line containing the execution point. 158 * <li> 159 * {@code "MyClass.mash(MyClass.java)"} - As above, but the line 160 * number is unavailable. 161 * <li> 162 * {@code "MyClass.mash(Unknown Source)"} - As above, but neither 163 * the file name nor the line number are available. 164 * <li> 165 * {@code "MyClass.mash(Native Method)"} - As above, but neither 166 * the file name nor the line number are available, and the method 167 * containing the execution point is known to be a native method. 168 * </ul> 169 * @see Throwable#printStackTrace() 170 */ toString()171 public String toString() { 172 return getClassName() + "." + methodName + 173 (isNativeMethod() ? "(Native Method)" : 174 (fileName != null && lineNumber >= 0 ? 175 "(" + fileName + ":" + lineNumber + ")" : 176 (fileName != null ? "("+fileName+")" : "(Unknown Source)"))); 177 } 178 179 /** 180 * Returns true if the specified object is another 181 * {@code StackTraceElement} instance representing the same execution 182 * point as this instance. Two stack trace elements {@code a} and 183 * {@code b} are equal if and only if: 184 * <pre>{@code 185 * equals(a.getFileName(), b.getFileName()) && 186 * a.getLineNumber() == b.getLineNumber()) && 187 * equals(a.getClassName(), b.getClassName()) && 188 * equals(a.getMethodName(), b.getMethodName()) 189 * }</pre> 190 * where {@code equals} has the semantics of {@link 191 * java.util.Objects#equals(Object, Object) Objects.equals}. 192 * 193 * @param obj the object to be compared with this stack trace element. 194 * @return true if the specified object is another 195 * {@code StackTraceElement} instance representing the same 196 * execution point as this instance. 197 */ equals(Object obj)198 public boolean equals(Object obj) { 199 if (obj==this) 200 return true; 201 if (!(obj instanceof StackTraceElement)) 202 return false; 203 StackTraceElement e = (StackTraceElement)obj; 204 return e.declaringClass.equals(declaringClass) && 205 e.lineNumber == lineNumber && 206 Objects.equals(methodName, e.methodName) && 207 Objects.equals(fileName, e.fileName); 208 } 209 210 /** 211 * Returns a hash code value for this stack trace element. 212 */ hashCode()213 public int hashCode() { 214 int result = 31*declaringClass.hashCode() + methodName.hashCode(); 215 result = 31*result + Objects.hashCode(fileName); 216 result = 31*result + lineNumber; 217 return result; 218 } 219 220 private static final long serialVersionUID = 6992337162326171013L; 221 } 222