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      */
  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     /**
  79      * Creates an empty stack frame element to be filled in by Throwable.
  80      * @since 1.9
  81      */
  82     StackTraceElement() { }
  83 
  84     /**
  85      * Returns the name of the source file containing the execution point
  86      * represented by this stack trace element.  Generally, this corresponds
  87      * to the {@code SourceFile} attribute of the relevant {@code class}
  88      * file (as per <i>The Java Virtual Machine Specification</i>, Section
  89      * 4.7.7).  In some systems, the name may refer to some source code unit
  90      * other than a file, such as an entry in source repository.
  91      *
  92      * @return the name of the file containing the execution point
  93      *         represented by this stack trace element, or {@code null} if
  94      *         this information is unavailable.
  95      */
  96     public String getFileName() {
  97         return fileName;
  98     }
  99 
 100     /**
 101      * Returns the line number of the source line containing the execution
 102      * point represented by this stack trace element.  Generally, this is
 103      * derived from the {@code LineNumberTable} attribute of the relevant
 104      * {@code class} file (as per <i>The Java Virtual Machine
 105      * Specification</i>, Section 4.7.8).
 106      *
 107      * @return the line number of the source line containing the execution
 108      *         point represented by this stack trace element, or a negative
 109      *         number if this information is unavailable.
 110      */
 111     public int getLineNumber() {
 112         return lineNumber;
 113     }
 114 
 115     /**
 116      * Returns the fully qualified name of the class containing the
 117      * execution point represented by this stack trace element.
 118      *
 119      * @return the fully qualified name of the {@code Class} containing
 120      *         the execution point represented by this stack trace element.
 121      */
 122     public String getClassName() {
 123         return declaringClass;
 124     }
 125 
 126     /**
 127      * Returns the name of the method containing the execution point
 128      * represented by this stack trace element.  If the execution point is
 129      * contained in an instance or class initializer, this method will return
 130      * the appropriate <i>special method name</i>, {@code <init>} or
 131      * {@code <clinit>}, as per Section 3.9 of <i>The Java Virtual
 132      * Machine Specification</i>.
 133      *
 134      * @return the name of the method containing the execution point
 135      *         represented by this stack trace element.
 136      */
 137     public String getMethodName() {
 138         return methodName;
 139     }
 140 
 141     /**
 142      * Returns true if the method containing the execution point
 143      * represented by this stack trace element is a native method.
 144      *
 145      * @return {@code true} if the method containing the execution point
 146      *         represented by this stack trace element is a native method.
 147      */
 148     public boolean isNativeMethod() {
 149         return lineNumber == -2;
 150     }
 151 
 152     /**
 153      * Returns a string representation of this stack trace element.  The
 154      * format of this string depends on the implementation, but the following
 155      * examples may be regarded as typical:
 156      * <ul>
 157      * <li>
 158      *   {@code "MyClass.mash(MyClass.java:9)"} - Here, {@code "MyClass"}
 159      *   is the <i>fully-qualified name</i> of the class containing the
 160      *   execution point represented by this stack trace element,
 161      *   {@code "mash"} is the name of the method containing the execution
 162      *   point, {@code "MyClass.java"} is the source file containing the
 163      *   execution point, and {@code "9"} is the line number of the source
 164      *   line containing the execution point.
 165      * <li>
 166      *   {@code "MyClass.mash(MyClass.java)"} - As above, but the line
 167      *   number is unavailable.
 168      * <li>
 169      *   {@code "MyClass.mash(Unknown Source)"} - As above, but neither
 170      *   the file name nor the line  number are available.
 171      * <li>
 172      *   {@code "MyClass.mash(Native Method)"} - As above, but neither
 173      *   the file name nor the line  number are available, and the method
 174      *   containing the execution point is known to be a native method.
 175      * </ul>
 176      * @see    Throwable#printStackTrace()
 177      */
 178     public String toString() {
 179         return getClassName() + "." + methodName +
 180             (isNativeMethod() ? "(Native Method)" :
 181              (fileName != null && lineNumber >= 0 ?
 182               "(" + fileName + ":" + lineNumber + ")" :
 183               (fileName != null ?  "("+fileName+")" : "(Unknown Source)")));
 184     }
 185 
 186     /**
 187      * Returns true if the specified object is another
 188      * {@code StackTraceElement} instance representing the same execution
 189      * point as this instance.  Two stack trace elements {@code a} and
 190      * {@code b} are equal if and only if:
 191      * <pre>{@code
 192      *     equals(a.getFileName(), b.getFileName()) &&
 193      *     a.getLineNumber() == b.getLineNumber()) &&
 194      *     equals(a.getClassName(), b.getClassName()) &&
 195      *     equals(a.getMethodName(), b.getMethodName())
 196      * }</pre>
 197      * where {@code equals} has the semantics of {@link
 198      * java.util.Objects#equals(Object, Object) Objects.equals}.
 199      *
 200      * @param  obj the object to be compared with this stack trace element.
 201      * @return true if the specified object is another
 202      *         {@code StackTraceElement} instance representing the same
 203      *         execution point as this instance.
 204      */
 205     public boolean equals(Object obj) {
 206         if (obj==this)
 207             return true;
 208         if (!(obj instanceof StackTraceElement))
 209             return false;
 210         StackTraceElement e = (StackTraceElement)obj;
 211         return e.declaringClass.equals(declaringClass) &&
 212             e.lineNumber == lineNumber &&
 213             Objects.equals(methodName, e.methodName) &&
 214             Objects.equals(fileName, e.fileName);
 215     }
 216 
 217     /**
 218      * Returns a hash code value for this stack trace element.
 219      */
 220     public int hashCode() {
 221         int result = 31*declaringClass.hashCode() + methodName.hashCode();
 222         result = 31*result + Objects.hashCode(fileName);
 223         result = 31*result + lineNumber;
 224         return result;
 225     }
 226 
 227     private static final long serialVersionUID = 6992337162326171013L;
 228 }