1 /*
2 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
3 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
4 *
5 *
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7 *
8 *
9 *
10 *
11 *
12 *
13 *
14 *
15 *
16 *
17 *
18 *
19 *
20 *
21 *
22 *
23 *
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 }
222