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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       * 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>{@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      */
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 }