1 /*
   2  * Copyright (c) 2000, 2010, 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      */
  69     public StackTraceElement(String declaringClass, String methodName,
  70                              String fileName, int lineNumber) {
  71         this.declaringClass = Objects.nonNull(declaringClass, "Declaring class is null");
  72         this.methodName     = Objects.nonNull(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      */
  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      */
 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      */
 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      */
 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      */
 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      */
 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>
 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      */
 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      */
 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 }