/*
* %W% %E%
*
* Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang;
/**
* An element in a stack trace, as returned by {@link
* Throwable#getStackTrace()}. Each element represents a single stack frame.
* All stack frames except for the one at the top of the stack represent
* a method invocation. The frame at the top of the stack represents the
* execution point at which the stack trace was generated. Typically,
* this is the point at which the throwable corresponding to the stack trace
* was created.
* 堆栈跟踪中的元素，它由 Throwable.getStackTrace() 返回。
* 每个元素表示单独的一个堆栈帧。所有的堆栈帧
*（堆栈顶部的那个堆栈帧除外） 都表示一个方法调用。
* 堆栈顶部的帧表示生成堆栈跟踪的执行点。通常，
* 这是创建对应于堆栈跟踪的 throwable 的点。
*
* @since 1.4
* @author Josh Bloch
*/
public final class StackTraceElement implements java.io.Serializable {
// Normally initialized by VM (public constructor added in 1.5)
private String declaringClass;
private String methodName;
private String fileName;
private int lineNumber;
/**
* Creates a stack trace element representing the specified execution
* point.
* 创建表示指定执行点的堆栈跟踪元素
*
* @param declaringClass the fully qualified name of the class containing
* the execution point represented by the stack trace element
* @param methodName the name of the method containing the execution point
* represented by the stack trace element
* @param fileName the name of the file containing the execution point
* represented by the stack trace element, or <tt>null</tt> if
* this information is unavailable
* @param lineNumber the line number of the source line containing the
* execution point represented by this stack trace element, or
* a negative number if this information is unavailable. A value
* of -2 indicates that the method containing the execution point
* is a native method
* @throws NullPointerException if <tt>declaringClass</tt> or
* <tt>methodName</tt> is null
* @since 1.5
*/
public StackTraceElement(String declaringClass, String methodName,
String fileName, int lineNumber) {
if (declaringClass == null)
throw new NullPointerException("Declaring class is null");
if (methodName == null)
throw new NullPointerException("Method name is null");
this.declaringClass = declaringClass;
this.methodName = methodName;
this.fileName = fileName;
this.lineNumber = lineNumber;
}
/**
* Returns the name of the source file containing the execution point
* represented by this stack trace element. Generally, this corresponds
* to the <tt>SourceFile</tt> attribute of the relevant <tt>class</tt>
* file (as per <i>The Java Virtual Machine Specification</i>, Section
* 4.7.7). In some systems, the name may refer to some source code unit
* other than a file, such as an entry in source repository.
*
* @return the name of the file containing the execution point
* represented by this stack trace element, or <tt>null</tt> if
* this information is unavailable.
*/
public String getFileName() {
return fileName;
}
/**
* Returns the line number of the source line containing the execution
* point represented by this stack trace element. Generally, this is
* derived from the <tt>LineNumberTable</tt> attribute of the relevant
* <tt>class</tt> file (as per <i>The Java Virtual Machine
* Specification</i>, Section 4.7.8).
*
* @return the line number of the source line containing the execution
* point represented by this stack trace element, or a negative
* number if this information is unavailable.
*/
public int getLineNumber() {
return lineNumber;
}
/**
* Returns the fully qualified name of the class containing the
* execution point represented by this stack trace element.
*
* @return the fully qualified name of the <tt>Class</tt> containing
* the execution point represented by this stack trace element.
*/
public String getClassName() {
return declaringClass;
}
/**
* Returns the name of the method containing the execution point
* represented by this stack trace element. If the execution point is
* contained in an instance or class initializer, this method will return
* the appropriate <i>special method name</i>, <tt><init></tt> or
* <tt><clinit></tt>, as per Section 3.9 of <i>The Java Virtual
* Machine Specification</i>.
*
* @return the name of the method containing the execution point
* represented by this stack trace element.
*/
public String getMethodName() {
return methodName;
}
/**
* Returns true if the method containing the execution point
* represented by this stack trace element is a native method.
*
* @return <tt>true</tt> if the method containing the execution point
* represented by this stack trace element is a native method.
*/
public boolean isNativeMethod() {
return lineNumber == -2;
}
/**
* Returns a string representation of this stack trace element. The
* format of this string depends on the implementation, but the following
* examples may be regarded as typical:
* <ul>
* <li>
* <tt>"MyClass.mash(MyClass.java:9)"</tt> - Here, <tt>"MyClass"</tt>
* is the <i>fully-qualified name</i> of the class containing the
* execution point represented by this stack trace element,
* <tt>"mash"</tt> is the name of the method containing the execution
* point, <tt>"MyClass.java"</tt> is the source file containing the
* execution point, and <tt>"9"</tt> is the line number of the source
* line containing the execution point.
* <li>
* <tt>"MyClass.mash(MyClass.java)"</tt> - As above, but the line
* number is unavailable.
* <li>
* <tt>"MyClass.mash(Unknown Source)"</tt> - As above, but neither
* the file name nor the line number are available.
* <li>
* <tt>"MyClass.mash(Native Method)"</tt> - As above, but neither
* the file name nor the line number are available, and the method
* containing the execution point is known to be a native method.
* </ul>
* @see Throwable#printStackTrace()
*/
public String toString() {
return getClassName() + "." + methodName +
(isNativeMethod() ? "(Native Method)" :
(fileName != null && lineNumber >= 0 ?
"(" + fileName + ":" + lineNumber + ")" :
(fileName != null ? "("+fileName+")" : "(Unknown Source)")));
}
/**
* Returns true if the specified object is another
* <tt>StackTraceElement</tt> instance representing the same execution
* point as this instance. Two stack trace elements <tt>a</tt> and
* <tt>b</tt> are equal if and only if:
* <pre>
* equals(a.getFileName(), b.getFileName()) &&
* a.getLineNumber() == b.getLineNumber()) &&
* equals(a.getClassName(), b.getClassName()) &&
* equals(a.getMethodName(), b.getMethodName())
* </pre>
* where <tt>equals</tt> is defined as:
* <pre>
* static boolean equals(Object a, Object b) {
* return a==b || (a != null && a.equals(b));
* }
* </pre>
*
* @param obj the object to be compared with this stack trace element.
* @return true if the specified object is another
* <tt>StackTraceElement</tt> instance representing the same
* execution point as this instance.
*/
public boolean equals(Object obj) {
if (obj==this)
return true;
if (!(obj instanceof StackTraceElement))
return false;
StackTraceElement e = (StackTraceElement)obj;
return e.declaringClass.equals(declaringClass) && e.lineNumber == lineNumber
&& eq(methodName, e.methodName) && eq(fileName, e.fileName);
}
private static boolean eq(Object a, Object b) {
return a==b || (a != null && a.equals(b));
}
/**
* Returns a hash code value for this stack trace element.
*/
public int hashCode() {
int result = 31*declaringClass.hashCode() + methodName.hashCode();
result = 31*result + (fileName == null ? 0 : fileName.hashCode());
result = 31*result + lineNumber;
return result;
}
private static final long serialVersionUID = 6992337162326171013L;
}
