/*

  * Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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  */

 package java.lang;

 import java.util.Objects;

 /**

  * 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.

  *

  * @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.

      *

      * @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 {@code null} 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 {@code declaringClass} or

      *         {@code methodName} is null

      * @since 1.5

      */

     public StackTraceElement(String declaringClass, String methodName,

                              String fileName, int lineNumber) {

         this.declaringClass = Objects.requireNonNull(declaringClass, "Declaring class is null");

         this.methodName     = Objects.requireNonNull(methodName, "Method name is null");

         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 {@code SourceFile} attribute of the relevant {@code class}

      * 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 {@code null} 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 {@code LineNumberTable} attribute of the relevant

      * {@code class} 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 {@code Class} 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>, {@code <init>} or

      * {@code <clinit>}, 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 {@code true} 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>

      *   {@code "MyClass.mash(MyClass.java:9)"} - Here, {@code "MyClass"}

      *   is the <i>fully-qualified name</i> of the class containing the

      *   execution point represented by this stack trace element,

      *   {@code "mash"} is the name of the method containing the execution

      *   point, {@code "MyClass.java"} is the source file containing the

      *   execution point, and {@code "9"} is the line number of the source

      *   line containing the execution point.

      * <li>

      *   {@code "MyClass.mash(MyClass.java)"} - As above, but the line

      *   number is unavailable.

      * <li>

      *   {@code "MyClass.mash(Unknown Source)"} - As above, but neither

      *   the file name nor the line  number are available.

      * <li>

      *   {@code "MyClass.mash(Native Method)"} - 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

      * {@code StackTraceElement} instance representing the same execution

      * point as this instance.  Two stack trace elements {@code a} and

      * {@code b} 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 {@code equals} has the semantics of {@link

      * java.util.Objects#equals(Object, Object) Objects.equals}.

      *

      * @param  obj the object to be compared with this stack trace element.

      * @return true if the specified object is another

      *         {@code StackTraceElement} 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 &&

             Objects.equals(methodName, e.methodName) &&

             Objects.equals(fileName, e.fileName);

     }

     /**

      * Returns a hash code value for this stack trace element.

      */

     public int hashCode() {

         int result = 31*declaringClass.hashCode() + methodName.hashCode();

         result = 31*result + Objects.hashCode(fileName);

         result = 31*result + lineNumber;

         return result;

     }

     private static final long serialVersionUID = 6992337162326171013L;

 }